After updating Ubuntu (apt-get update, apt-get upgrade and apt-get dist-upgrade) last Tuesday, GDM stopped working, and the startup hangs on the Ubuntu logo. Lightdm also don't work (same happens). If I start GDM manually from commandline, it opens and shows the time, accessibility options, and so on, but with no login and password form; and if I start Lightdm, it opens in low-graphics mode and the mouse cursor doesn't appear. So I used the TTY console to install KDM, which works as expected.

I've tried to purge and reinstall both GDM and Lightdm, but no success.
Editing /etc/X11/default-display-manager, using dpkg-reconfigure, dpkg --configure -a also didn't help.

(I have Ubuntu 14.04 with Xfce desktop and had GDM as display manager. Dual boot with Windows 7.)

These are the logs I believe that can be useful, but I can post other logs if needed:

This is the part of dpkg.log that lists the updates done that day:

2014-05-20 00:33:02 startup archives unpack

2014-05-20 00:33:15 upgrade vlc-plugin-pulse:i386 2.1.2-2build2 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:15 status half-configured vlc-plugin-pulse:i386 2.1.2-2build2

2014-05-20 00:33:15 status unpacked vlc-plugin-pulse:i386 2.1.2-2build2

2014-05-20 00:33:15 status half-installed vlc-plugin-pulse:i386 2.1.2-2build2

2014-05-20 00:33:15 status triggers-pending vlc-nox:i386 2.1.2-2build2

2014-05-20 00:33:15 status half-installed vlc-plugin-pulse:i386 2.1.2-2build2

2014-05-20 00:33:16 status half-installed vlc-plugin-pulse:i386 2.1.2-2build2

2014-05-20 00:33:16 status unpacked vlc-plugin-pulse:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:16 status unpacked vlc-plugin-pulse:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:16 upgrade vlc-plugin-notify:i386 2.1.2-2build2 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:16 status half-configured vlc-plugin-notify:i386 2.1.2-2build2

2014-05-20 00:33:16 status unpacked vlc-plugin-notify:i386 2.1.2-2build2

2014-05-20 00:33:16 status half-installed vlc-plugin-notify:i386 2.1.2-2build2

2014-05-20 00:33:16 status half-installed vlc-plugin-notify:i386 2.1.2-2build2

2014-05-20 00:33:16 status half-installed vlc-plugin-notify:i386 2.1.2-2build2

2014-05-20 00:33:17 status unpacked vlc-plugin-notify:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:17 status unpacked vlc-plugin-notify:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:17 upgrade vlc:i386 2.1.2-2build2 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:17 status half-configured vlc:i386 2.1.2-2build2

2014-05-20 00:33:17 status unpacked vlc:i386 2.1.2-2build2

2014-05-20 00:33:17 status half-installed vlc:i386 2.1.2-2build2

2014-05-20 00:33:17 status triggers-pending mime-support:all 3.54ubuntu1

2014-05-20 00:33:17 status half-installed vlc:i386 2.1.2-2build2

2014-05-20 00:33:18 status triggers-pending man-db:i386 2.6.7.1-1

2014-05-20 00:33:18 status triggers-pending bamfdaemon:i386 0.5.1+14.04.20140409-0ubuntu1

2014-05-20 00:33:18 status half-installed vlc:i386 2.1.2-2build2

2014-05-20 00:33:18 status triggers-pending desktop-file-utils:i386 0.22-1ubuntu1

2014-05-20 00:33:18 status half-installed vlc:i386 2.1.2-2build2

2014-05-20 00:33:18 status triggers-pending gnome-menus:i386 3.10.1-0ubuntu2

2014-05-20 00:33:18 status triggers-pending mime-support:all 3.54ubuntu1

2014-05-20 00:33:18 status half-installed vlc:i386 2.1.2-2build2

2014-05-20 00:33:18 status unpacked vlc:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:18 status unpacked vlc:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:19 upgrade libvlccore7:i386 2.1.2-2build2 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:19 status half-configured libvlccore7:i386 2.1.2-2build2

2014-05-20 00:33:19 status unpacked libvlccore7:i386 2.1.2-2build2

2014-05-20 00:33:19 status half-installed libvlccore7:i386 2.1.2-2build2

2014-05-20 00:33:19 status half-installed libvlccore7:i386 2.1.2-2build2

2014-05-20 00:33:19 status unpacked libvlccore7:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:19 status unpacked libvlccore7:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:20 upgrade vlc-data:all 2.1.2-2build2 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:20 status half-configured vlc-data:all 2.1.2-2build2

2014-05-20 00:33:20 status unpacked vlc-data:all 2.1.2-2build2

2014-05-20 00:33:20 status half-installed vlc-data:all 2.1.2-2build2

2014-05-20 00:33:21 status triggers-pending hicolor-icon-theme:all 0.13-1

2014-05-20 00:33:21 status half-installed vlc-data:all 2.1.2-2build2

2014-05-20 00:33:23 status half-installed vlc-data:all 2.1.2-2build2

2014-05-20 00:33:23 status unpacked vlc-data:all 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:23 status unpacked vlc-data:all 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:24 upgrade vlc-nox:i386 2.1.2-2build2 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:24 status half-configured vlc-nox:i386 2.1.2-2build2

2014-05-20 00:33:24 status unpacked vlc-nox:i386 2.1.2-2build2

2014-05-20 00:33:24 status half-installed vlc-nox:i386 2.1.2-2build2

2014-05-20 00:33:25 status half-installed vlc-nox:i386 2.1.2-2build2

2014-05-20 00:33:25 status unpacked vlc-nox:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:25 status unpacked vlc-nox:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:26 upgrade libvlc5:i386 2.1.2-2build2 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:26 status half-configured libvlc5:i386 2.1.2-2build2

2014-05-20 00:33:26 status unpacked libvlc5:i386 2.1.2-2build2

2014-05-20 00:33:26 status half-installed libvlc5:i386 2.1.2-2build2

2014-05-20 00:33:26 status half-installed libvlc5:i386 2.1.2-2build2

2014-05-20 00:33:26 status unpacked libvlc5:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:26 status unpacked libvlc5:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:27 upgrade network-manager-gnome:i386 0.9.8.8-0ubuntu4 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:27 status half-configured network-manager-gnome:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:27 status unpacked network-manager-gnome:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:27 status half-installed network-manager-gnome:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:27 status triggers-pending gconf2:i386 3.2.6-0ubuntu2

2014-05-20 00:33:27 status half-installed network-manager-gnome:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:27 status triggers-pending libglib2.0-0:i386 2.40.0-2

2014-05-20 00:33:27 status half-installed network-manager-gnome:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:27 status half-installed network-manager-gnome:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:27 status half-installed network-manager-gnome:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:27 status half-installed network-manager-gnome:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:28 status half-installed network-manager-gnome:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:28 status unpacked network-manager-gnome:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:28 status unpacked network-manager-gnome:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:28 upgrade libnm-gtk-dev:i386 0.9.8.8-0ubuntu4 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:28 status half-configured libnm-gtk-dev:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:28 status unpacked libnm-gtk-dev:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:28 status half-installed libnm-gtk-dev:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:28 status half-installed libnm-gtk-dev:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:28 status unpacked libnm-gtk-dev:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:29 status unpacked libnm-gtk-dev:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:29 upgrade libnm-gtk0:i386 0.9.8.8-0ubuntu4 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:29 status half-configured libnm-gtk0:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:29 status unpacked libnm-gtk0:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:29 status half-installed libnm-gtk0:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:29 status half-installed libnm-gtk0:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:29 status unpacked libnm-gtk0:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:29 status unpacked libnm-gtk0:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:30 upgrade libnm-gtk-common:all 0.9.8.8-0ubuntu4 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:30 status half-configured libnm-gtk-common:all 0.9.8.8-0ubuntu4

2014-05-20 00:33:30 status unpacked libnm-gtk-common:all 0.9.8.8-0ubuntu4

2014-05-20 00:33:30 status half-installed libnm-gtk-common:all 0.9.8.8-0ubuntu4

2014-05-20 00:33:30 status half-installed libnm-gtk-common:all 0.9.8.8-0ubuntu4

2014-05-20 00:33:30 status unpacked libnm-gtk-common:all 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:30 status unpacked libnm-gtk-common:all 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:30 upgrade gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:30 status half-configured gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:31 status unpacked gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:31 status half-installed gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:31 status half-installed gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4

2014-05-20 00:33:31 status unpacked gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:31 status unpacked gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:31 trigproc mime-support:all 3.54ubuntu1 3.54ubuntu1

2014-05-20 00:33:31 status half-configured mime-support:all 3.54ubuntu1

2014-05-20 00:33:36 status installed mime-support:all 3.54ubuntu1

2014-05-20 00:33:36 trigproc man-db:i386 2.6.7.1-1 2.6.7.1-1

2014-05-20 00:33:36 status half-configured man-db:i386 2.6.7.1-1

2014-05-20 00:33:39 status installed man-db:i386 2.6.7.1-1

2014-05-20 00:33:39 trigproc bamfdaemon:i386 0.5.1+14.04.20140409-0ubuntu1 0.5.1+14.04.20140409-0ubuntu1

2014-05-20 00:33:39 status half-configured bamfdaemon:i386 0.5.1+14.04.20140409-0ubuntu1

2014-05-20 00:33:39 status installed bamfdaemon:i386 0.5.1+14.04.20140409-0ubuntu1

2014-05-20 00:33:39 trigproc desktop-file-utils:i386 0.22-1ubuntu1 0.22-1ubuntu1

2014-05-20 00:33:39 status half-configured desktop-file-utils:i386 0.22-1ubuntu1

2014-05-20 00:33:40 status installed desktop-file-utils:i386 0.22-1ubuntu1

2014-05-20 00:33:40 trigproc gnome-menus:i386 3.10.1-0ubuntu2 3.10.1-0ubuntu2

2014-05-20 00:33:40 status half-configured gnome-menus:i386 3.10.1-0ubuntu2

2014-05-20 00:33:40 status installed gnome-menus:i386 3.10.1-0ubuntu2

2014-05-20 00:33:40 trigproc hicolor-icon-theme:all 0.13-1 0.13-1

2014-05-20 00:33:40 status half-configured hicolor-icon-theme:all 0.13-1

2014-05-20 00:33:45 status installed hicolor-icon-theme:all 0.13-1

2014-05-20 00:33:45 trigproc gconf2:i386 3.2.6-0ubuntu2 3.2.6-0ubuntu2

2014-05-20 00:33:45 status half-configured gconf2:i386 3.2.6-0ubuntu2

2014-05-20 00:33:45 status installed gconf2:i386 3.2.6-0ubuntu2

2014-05-20 00:33:45 trigproc libglib2.0-0:i386 2.40.0-2 2.40.0-2

2014-05-20 00:33:45 status half-configured libglib2.0-0:i386 2.40.0-2

2014-05-20 00:33:47 status installed libglib2.0-0:i386 2.40.0-2

2014-05-20 00:33:47 startup packages configure

2014-05-20 00:33:47 configure vlc-data:all 2.1.4-0ubuntu14.04.1 <none>

2014-05-20 00:33:47 status unpacked vlc-data:all 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:47 status half-configured vlc-data:all 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status installed vlc-data:all 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 configure libvlccore7:i386 2.1.4-0ubuntu14.04.1 <none>

2014-05-20 00:33:48 status unpacked libvlccore7:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status half-configured libvlccore7:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status installed libvlccore7:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status triggers-pending libc-bin:i386 2.19-0ubuntu6

2014-05-20 00:33:48 configure libvlc5:i386 2.1.4-0ubuntu14.04.1 <none>

2014-05-20 00:33:48 status unpacked libvlc5:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status half-configured libvlc5:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status installed libvlc5:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 configure vlc-nox:i386 2.1.4-0ubuntu14.04.1 <none>

2014-05-20 00:33:48 status unpacked vlc-nox:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status half-configured vlc-nox:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status installed vlc-nox:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 configure vlc-plugin-pulse:i386 2.1.4-0ubuntu14.04.1 <none>

2014-05-20 00:33:48 status unpacked vlc-plugin-pulse:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status half-configured vlc-plugin-pulse:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status installed vlc-plugin-pulse:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 configure vlc-plugin-notify:i386 2.1.4-0ubuntu14.04.1 <none>

2014-05-20 00:33:48 status unpacked vlc-plugin-notify:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status half-configured vlc-plugin-notify:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 status installed vlc-plugin-notify:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:48 configure vlc:i386 2.1.4-0ubuntu14.04.1 <none>

2014-05-20 00:33:48 status unpacked vlc:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:49 status half-configured vlc:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:49 status installed vlc:i386 2.1.4-0ubuntu14.04.1

2014-05-20 00:33:49 configure libnm-gtk-common:all 0.9.8.8-0ubuntu4.1 <none>

2014-05-20 00:33:49 status unpacked libnm-gtk-common:all 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status half-configured libnm-gtk-common:all 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status installed libnm-gtk-common:all 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 configure libnm-gtk0:i386 0.9.8.8-0ubuntu4.1 <none>

2014-05-20 00:33:49 status unpacked libnm-gtk0:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status half-configured libnm-gtk0:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status installed libnm-gtk0:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 configure network-manager-gnome:i386 0.9.8.8-0ubuntu4.1 <none>

2014-05-20 00:33:49 status unpacked network-manager-gnome:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status unpacked network-manager-gnome:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status half-configured network-manager-gnome:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status installed network-manager-gnome:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 configure gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4.1 <none>

2014-05-20 00:33:49 status unpacked gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status half-configured gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status installed gir1.2-nmgtk-1.0:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 configure libnm-gtk-dev:i386 0.9.8.8-0ubuntu4.1 <none>

2014-05-20 00:33:49 status unpacked libnm-gtk-dev:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status half-configured libnm-gtk-dev:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 status installed libnm-gtk-dev:i386 0.9.8.8-0ubuntu4.1

2014-05-20 00:33:49 trigproc libc-bin:i386 2.19-0ubuntu6 <none>

2014-05-20 00:33:49 status half-configured libc-bin:i386 2.19-0ubuntu6

2014-05-20 00:33:50 status installed libc-bin:i386 2.19-0ubuntu6

Contents of boot.log when I select GDM as default:

resume: libgcrypt version: 1.5.3

 * Starting Mount filesystems on boot [ OK ]

 * Starting Fix-up sensitive /proc filesystem entries [ OK ]

 * Starting Populate /dev filesystem [ OK ]

 * Starting Populate and link to /run filesystem [ OK ]

 * Stopping Fix-up sensitive /proc filesystem entries [ OK ]

 * Stopping Populate /dev filesystem [ OK ]

 * Stopping Populate and link to /run filesystem [ OK ]

 * Stopping Track if upstart is running in a container [ OK ]

 * Starting Initialize or finalize resolvconf [ OK ]

 * Starting set console keymap [ OK ]

 * Starting Signal sysvinit that virtual filesystems are mounted [ OK ]

 * Starting Signal sysvinit that virtual filesystems are mounted [ OK ]

 * Starting set sysctls from /etc/sysctl.conf [ OK ]

 * Starting Bridge udev events into upstart [ OK ]

 * Stopping set console keymap [ OK ]

 * Starting Signal sysvinit that remote filesystems are mounted [ OK ]

 * Stopping set sysctls from /etc/sysctl.conf [ OK ]

 * Starting device node and kernel event manager [ OK ]

 * Starting load modules from /etc/modules [ OK ]

 * Starting cold plug devices [ OK ]

 * Starting log initial device creation [ OK ]

 * Stopping load modules from /etc/modules [ OK ]

 * Starting configure network device security [ OK ]

 * Starting configure network device security [ OK ]

 * Starting Mount network filesystems [ OK ]

 * Stopping Mount network filesystems [ OK ]

 * Starting Bridge socket events into upstart [ OK ]

 * Starting Signal sysvinit that the rootfs is mounted [ OK ]

 * Starting configure network device [ OK ]

 * Starting Uncomplicated firewall [ OK ]

 * Starting configure network device [ OK ]

 * Starting Clean /tmp directory [ OK ]

 * Stopping Clean /tmp directory [ OK ]

 * Stopping Read required files in advance (for other mountpoints) [ OK ]

 * Stopping cold plug devices [ OK ]

 * Stopping log initial device creation [ OK ]

 * Starting enable remaining boot-time encrypted block devices [ OK ]

 * Starting Signal sysvinit that local filesystems are mounted [ OK ]

 * Starting restore software rfkill state [ OK ]

 * Starting SMB/CIFS File Server [ OK ]

 * Starting configure network device security [ OK ]

 * Stopping Mount filesystems on boot [ OK ]

 * Stopping restore software rfkill state [ OK ]

 * Starting Enabling additional executable binary formats [ OK ]

 * Starting flush early job output to logs [ OK ]

 * Stopping Failsafe Boot Delay [ OK ]

 * Starting System V initialisation compatibility [ OK ]

 * Stopping flush early job output to logs [ OK ]

 * Starting configure virtual network devices [ OK ]

 * Starting Bridge file events into upstart [ OK ]

 * Starting early crypto disks...         

 [ OK ]

 * Starting system logging daemon [ OK ]

Skipping profile in /etc/apparmor.d/disable: usr.bin.firefox

Skipping profile in /etc/apparmor.d/disable: usr.sbin.rsyslogd

 * Starting AppArmor profiles         

 [ OK ]

 * Setting sensors limits         

 [ OK ]

 * Starting SMB/CIFS File and Active Directory Server [ OK ]

 * Starting D-Bus system message bus [ OK ]

 * Stopping System V initialisation compatibility [ OK ]

 * Starting modem connection manager [ OK ]

 * Starting configure network device security [ OK ]

 * Starting SystemD login management service [ OK ]

 * Starting System V runlevel compatibility [ OK ]

 * Starting GNOME Display Manager [ OK ]

 * Starting ACPI daemon [ OK ]

 * Starting anac(h)ronistic cron [ OK ]

 * Starting K Display Manager [ OK ]

 * Starting save kernel messages [ OK ]

 * Starting regular background program processing daemon [ OK ]

 * Starting deferred execution scheduler [ OK ]

 * Stopping save kernel messages [ OK ]

 * Stopping anac(h)ronistic cron [ OK ]

 * Starting bluetooth daemon [ OK ]

 * Starting crash report submission daemon [ OK ]

 * speech-dispatcher disabled; edit /etc/default/speech-dispatcher

 * Stopping CPU interrupts balancing daemon [ OK ]

 * Starting GNOME Display Manager [ fail ]

 * Starting automatic crash report generation [ OK ]

 * Starting cups-browsed - Bonjour remote printer browsing daemon [ OK ]

 * Stopping Restore Sound Card State [ OK ]

 * Starting SMB/CIFS File and Active Directory Server [ fail ]

 * Stopping Send an event to indicate plymouth is up [ OK ]

 * Stopping K Display Manager [ OK ]

 * Starting network connection manager [ OK ]

Starting VirtualBox kernel modules * Starting CUPS printing spooler/server [ OK ]

 * Starting Samba Auto-reload Integration [ OK ]

 * Stopping Samba Auto-reload Integration [ OK ]

 ...done.

 * Starting NTP server ntpd         

 [ OK ]

saned disabled; edit /etc/default/saned

 * Stopping System V runlevel compatibility [ OK ]

 * Stopping TeamViewer remote control daemon [ OK ]

 * Starting Mount network filesystems [ OK ]

 * Starting Samba Winbind [ OK ]

 * Stopping Mount network filesystems [ OK ]

 * Starting NetBIOS name server [ OK ]

 * Stopping LightDM Display Manager [ OK ]

 * Stopping Read required files in advance [ OK ]

Contents of boot.log when I select Lightdm as default:

resume: libgcrypt version: 1.5.3

 * Stopping Read required files in advance [ OK ]

 * Starting Mount filesystems on boot [ OK ]

 * Starting Populate and link to /run filesystem [ OK ]

 * Stopping Populate and link to /run filesystem [ OK ]

 * Starting Initialize or finalize resolvconf [ OK ]

 * Stopping Track if upstart is running in a container [ OK ]

 * Starting Signal sysvinit that virtual filesystems are mounted [ OK ]

 * Starting Signal sysvinit that virtual filesystems are mounted [ OK ]

 * Starting Bridge udev events into upstart [ OK ]

 * Starting Signal sysvinit that remote filesystems are mounted [ OK ]

 * Starting device node and kernel event manager [ OK ]

 * Starting load modules from /etc/modules [ OK ]

 * Starting cold plug devices [ OK ]

 * Starting log initial device creation [ OK ]

 * Stopping load modules from /etc/modules [ OK ]

 * Starting Signal sysvinit that the rootfs is mounted [ OK ]

 * Starting Clean /tmp directory [ OK ]

 * Starting configure network device security [ OK ]

 * Stopping Clean /tmp directory [ OK ]

 * Starting Uncomplicated firewall [ OK ]

 * Starting configure network device [ OK ]

 * Starting configure network device security [ OK ]

 * Starting Mount network filesystems [ OK ]

 * Stopping Mount network filesystems [ OK ]

 * Starting configure network device [ OK ]

 * Starting Bridge socket events into upstart [ OK ]

 * Stopping cold plug devices [ OK ]

 * Stopping log initial device creation [ OK ]

 * Starting enable remaining boot-time encrypted block devices [ OK ]

 * Stopping Read required files in advance (for other mountpoints) [ OK ]

 * Starting SMB/CIFS File Server [ OK ]

 * Starting Signal sysvinit that local filesystems are mounted [ OK ]

 * Starting configure network device security [ OK ]

 * Stopping Mount filesystems on boot [ OK ]

 * Starting Enabling additional executable binary formats [ OK ]

 * Starting flush early job output to logs [ OK ]

 * Stopping Failsafe Boot Delay [ OK ]

 * Starting D-Bus system message bus [ OK ]

 * Starting System V initialisation compatibility [ OK ]

 * Stopping flush early job output to logs [ OK ]

 * Starting modem connection manager [ OK ]

 * Starting configure network device security [ OK ]

 * Starting early crypto disks...         

 [ OK ]

 * Starting bluetooth daemon [ OK ]

 * Starting configure virtual network devices [ OK ]

 * Starting system logging daemon [ OK ]

 * Starting SystemD login management service [ OK ]

 * Starting Bridge file events into upstart [ OK ]

 * Starting SMB/CIFS File and Active Directory Server [ OK ]

Skipping profile in /etc/apparmor.d/disable: usr.bin.firefox

Skipping profile in /etc/apparmor.d/disable: usr.sbin.rsyslogd

 * Starting AppArmor profiles         

 [ OK ]

 * Starting network connection manager [ OK ]

 * Starting SMB/CIFS File and Active Directory Server [ fail ]

 * Setting sensors limits        * Starting CUPS printing spooler/server [ OK ]



 [ OK ]

 * Starting Samba Auto-reload Integration [ OK ]

 * Stopping Samba Auto-reload Integration [ OK ]

 * Starting cups-browsed - Bonjour remote printer browsing daemon [ OK ]

 * Stopping System V initialisation compatibility [ OK ]

 * speech-dispatcher disabled; edit /etc/default/speech-dispatcher

 * Starting System V runlevel compatibility [ OK ]

 * Starting ACPI daemon [ OK ]

 * Starting anac(h)ronistic cron [ OK ]

 * Starting K Display Manager [ OK ]

 * Starting save kernel messages [ OK ]

 * Starting crash report submission daemon [ OK ]

 * Starting regular background program processing daemon [ OK ]

 * Starting deferred execution scheduler [ OK ]

 * Stopping save kernel messages [ OK ]

 * Stopping anac(h)ronistic cron [ OK ]

 * Stopping CPU interrupts balancing daemon [ OK ]

 * Starting automatic crash report generation [ OK ]

 * Stopping Restore Sound Card State [ OK ]

 * Stopping Send an event to indicate plymouth is up [ OK ]

 * Stopping TeamViewer remote control daemon [ OK ]

 * Stopping K Display Manager [ OK ]

 * Starting Mount network filesystems [ OK ]

 * Starting Samba Winbind [ OK ]

 * Stopping Mount network filesystems [ OK ]

 * Starting NetBIOS name server [ OK ]

Starting VirtualBox kernel modules ...done.

 * Starting NTP server ntpd         

 [ OK ]

saned disabled; edit /etc/default/saned

 * Stopping System V runlevel compatibility [ OK ]

 * Stopping LightDM Display Manager [ OK ]

Finally, contents of boot.log when I set the default to KDM (the only one that is working):

resume: libgcrypt version: 1.5.3

 * Stopping Read required files in advance [ OK ]

 * Starting Mount filesystems on boot [ OK ]

 * Starting Populate /dev filesystem [ OK ]

 * Starting Populate and link to /run filesystem [ OK ]

 * Stopping Populate /dev filesystem [ OK ]

 * Stopping Populate and link to /run filesystem [ OK ]

 * Stopping Track if upstart is running in a container [ OK ]

 * Starting Initialize or finalize resolvconf [ OK ]

 * Starting set console keymap [ OK ]

 * Starting Signal sysvinit that virtual filesystems are mounted [ OK ]

 * Starting Signal sysvinit that virtual filesystems are mounted [ OK ]

 * Starting Bridge udev events into upstart [ OK ]

 * Stopping set console keymap [ OK ]

 * Starting Signal sysvinit that remote filesystems are mounted [ OK ]

 * Starting device node and kernel event manager [ OK ]

 * Starting load modules from /etc/modules [ OK ]

 * Starting cold plug devices [ OK ]

 * Starting log initial device creation [ OK ]

 * Stopping load modules from /etc/modules [ OK ]

 * Starting configure network device security [ OK ]

 * Starting Signal sysvinit that the rootfs is mounted [ OK ]

 * Stopping Read required files in advance (for other mountpoints) [ OK ]

 * Starting Clean /tmp directory [ OK ]

 * Stopping Clean /tmp directory [ OK ]

 * Starting Uncomplicated firewall [ OK ]

 * Starting configure network device [ OK ]

 * Stopping Read required files in advance (for other mountpoints) [ OK ]

 * Starting Signal sysvinit that local filesystems are mounted [ OK ]

 * Stopping Mount filesystems on boot [ OK ]

 * Starting Enabling additional executable binary formats [ OK ]

 * Starting flush early job output to logs [ OK ]

 * Starting configure network device security [ OK ]

 * Starting D-Bus system message bus [ OK ]

 * Stopping flush early job output to logs [ OK ]

 * Starting SystemD login management service [ OK ]

 * Starting bluetooth daemon [ OK ]

 * Starting system logging daemon [ OK ]

 * Starting Mount network filesystems [ OK ]

 * Starting Failsafe Boot Delay [ OK ]

 * Starting SMB/CIFS File Server [ OK ]

 * Stopping Failsafe Boot Delay [ OK ]

 * Stopping Mount network filesystems [ OK ]

 * Starting System V initialisation compatibility [ OK ]

 * Starting modem connection manager [ OK ]

 * Starting configure network device security [ OK ]

 * Starting configure network device [ OK ]

 * Starting early crypto disks...         

 [ OK ]

 * Starting Bridge file events into upstart [ OK ]

 * Starting Bridge socket events into upstart [ OK ]

Skipping profile in /etc/apparmor.d/disable: usr.bin.firefox

Skipping profile in /etc/apparmor.d/disable: usr.sbin.rsyslogd

 * Starting AppArmor profiles         

 [ OK ]

 * Setting sensors limits         

 [ OK ]

 * Starting network connection manager [ OK ]

 * Starting SMB/CIFS File and Active Directory Server [ OK ]

 * Starting CUPS printing spooler/server [ OK ]

 * Stopping cold plug devices [ OK ]

 * Stopping System V initialisation compatibility [ OK ]

 * Starting Samba Auto-reload Integration [ OK ]

How can I fix this?