Whats your GUI? If it's KDE, try clicking on the gray background and selecting exit. Then run 'startkde' from the console.
If that works, then type
echo "exec startkde" > ~/.xinitrc
echo "exec startkde" > /etc/X11/xinit/xinitrc (I think this is the location of the file. Have a look and try and find it first. It'll be something called xinitrc or .xinitrc in a similar location)
If you use gnome, follow the above instructions, but use "gnome-session" everywhere where "startkde" occurs.
Hope that helps