Ubuntu 12.04 boots to TTY1
or try to use this command:
startx
I have had the same problem, and you can install the ubuntu again by typing.
Sudo apt-get update
Sudo apt-get install --reinstall ubuntu-desktop
startx
And it should work.
EDIT: line 2 should install ubuntu-desktop (with a dash), not ubuntu desktop.
You could use this command to turn the Xserver back on.
sudo systemctl set-default graphical.target
Just for future problems.
I did this:
sudo apt-get update
sudo apt-get install --reinstall ubuntu-desktop
startx