OK. It's quite a rarity for Linux to go down so badly that you have to hard-reboot to fix the problem. Firstly, try setting up your X configuration to the lowest possible demonination (640x480x16 generic VGA isn't it?). If this runs, try the next one up. Oh, and make sure that you back up the files between each one. Eventually you should have reached a reasonable setup. If, however, you still just get blank screens, try pressing CTRL-ALT-BACKSPACE. This should close the X server and dump you back at the command line. If not, try pressing CTRL-ALT-F1 (or F2, or whatever). If you manually types startx, then ctrl-alt-f1 should show you the X logging, in which case, just press CTRL-C to close X.
Any more probs, just post.