I just did a fresh install of Ubuntu 13.10 64bit, and it says that I have 2 monitors, when I actually only have one
I have a Dell XPS 15 with Nvidia graphics card if that helps in anyway
I am not an expert but I had the same problem. I have finally find the solution on this forum (here).
First, enter xrandr in your terminal. You will see that there are several outputs which are connected. The LVDS1 is your laptop's screen.
Normally, there is another outpout called VGA-1 orVGA-2 which is also connected. You have to note the name of this output.
Then, edit your grub with gksudo gedit /etc/default/grub and add video=VGA-1:d (VGA-1 is the name of the wrong output) in the GRUB_CMDLINE_LINUX line (you must have something like GRUB_CMDLINE_LINUX="video=VGA-1:d").
If your output is called like VGA-1-1, set video=VGA-1:d (setting video=VGA-1-1:d won't work).
If your output is called like VGA-1-2, set video=VGA-2:d (setting video=VGA-1-2:d or video=VGA-1:d does not seem to work, although one may still try them out separately to be certain).
Then update your grub with sudo update-grub and reboot.
