Here is another idea. If you have a linux emergency boot disk, you can insert it and you'll boot into that disk. Once you do that, you can change to the right directory and configuration file where it is determined whether or not to start up gnome automatically. You can make it NOT automatically start up gnome. At that point you can go the the configuration file where the vertical and horizontal refresh rates are set and you can fix them. This is dangerous if you make a mistake, but it is the last ditch effort. That's what I'm talking about.