sudo dpkg-reconfigure xserver-xorg

This will fire up the configurations for your XServer and will attempt
detecting the monitors supported display modes. On recent hardware
this should work, but it won't hurt to have your displays manual handy
just in case. You need to know the native resolution for your flat
panel.

After reconfiguration the xorg X11 server, run:

sudo /etc/init.d/gdm restart

This will restart the display manager and if everything is now set
properly, you'll get your familiar GUI login screen.

-- 
Andrew S. Zbikowski | http://andy.zibnet.us
IT Outhouse Blog Thing | http://www.itouthouse.com