Try CTRL-ALT-F1 and login as your favorite root user, and have fun
finding what's wrong by tailing the log files (X startup log).
Probably a tmp file keeping it from starting up, I had the same trouble
with my wife's machine and it had a temp file that would not allow X to go,
I removed it and it went okey dokey.  Need to get my daughter to stop 
thinking the glowing lights on the front of the box mean that you "don't" 
push the button!

Kelly Black
KB0GBJ