I'm far away from this computer, so First, switch to a console (Ctrl-Alt-1) First, slay gdm (hard when you can't see the pid using ps -A, so redirect the output to a file and use vi to fiddle with it) Then run Xorg -configure Edit the ~/xorg.conf.new Fix the HorizSync and VertRefresh under the Monitors section Disable Hardware Acceleration Test the new configuration using Xorg -config ~/xorg.conf.new Replace your real xorg.conf with ~/xorg.conf.new
You should have a nice, non crashing X Server with Gnome Desktop.