Does pressing "F8" during boot and going to "Safe Mode". Use System Restore.
Have you tried using a different video card or integrated graphics?
If that doesn't work, you can always do a fresh Windows Install. Windows 7 will install without reformatting move all your files to a folder called "Windows.old". That's faster than most troubleshooting if it's just a software error.
I tried to re-install Windows 7 without reformatting in order to safe my files (many of which were not backed-up) but it said it can't find the hard-drive. Do you know if I can extract the files on my hard-drive and copy them to an external hard-drive, without using my computer?
The local computer shop told me that if they do a recovery of my files, there is a minimum charge of $180.