I had that problem one day. it took me off guard. it happened after Battlefield 2 did some crtazy stuff with my video settings, therefore changing some things that I didn't want to be changed. Next time i loaded the computer, it freaked out. I had to go into the computer in safe mode (by holding F8 or F5 during the loading) and that allowed me to roll back the video drivers. I can't remember exactly what brought it back. I think i uninstalled Battlefield 2, too. But going in through safe mode was what saved me.