Press CTRL+ALT+F2, and then login as root (if your system can do this, otherwise login as your user, but then put sudo in front of the commands listed below EACH time). Then run these commands:
Code:
/etc/init.d/gdm stop
/etc/init.d/gdm3 stop
/etc/init.d/kdm stop
/etc/init.d/xdm stop
cd /etc/X11/
Xorg -configure
Once that completes, hit CTRL-ALT-DELETE.