From your post on Ubuntu Forums

Boot into Recovery mode and type this for the var/apt/cache error:

sudo mount -n -o remount /

Then disable auto login from virtual console by doing the following

sudo nano /etc/lightdm/lightdm.conf

Some of the lines should look like this

[SeatDefaults]

autologin-guest=false

autologin-user=username

autologin-user-timeout=0

autologin-session=lightdm-autologin

greeter-session=unity-greeter

user-session=ubuntu

Just put a # before all lines starting with autologin

Then whenever you boot into Ubuntu just change the login to unity from the lightdm's login screen options

Also you might want to remove Cinnamon

Then type in the terminal

sudo apt-get --purge autoremove cinnamon

Hope that helps.