OK, the only thing I can come up with is a Video card driver setting. Have you uninstalled your vid drivers. Using the uninstall found at -
http://www.guru3d.com/files/
Also have you done anything with the video card itself? over clocking adjusting the settings. using a refresh fix.
If so set these all back to default and see what happens. Could also be just a bad install. Check out Bazooka_joe's uninstall guide located at
http://mohaa.exe/joe/installguide.htm
Hope this helps. I wish I could be more helpful but this is a tricky one.
Good luck