Knoppix is a Linux distro that will run off the CD. Just stick the CD in, turn the PC on, and it boots into a fully working linux OS. Which is nice, but the best use is that you can test your system with it; If Windows is the problem, Knoppix will still work. So you could try that - Although it is a 700MB Download.
The other thing to do would be to swap GFX cards with someone to eliminate that as the source of the problem.
Can you do "Safe Mode: Command prompt only"? Booting to the command prompt won't change the resolution, so you could test your GFX card theory that way.
EDIT: Also, using Knoppix, you could save your data and write it to CD, then you could format the HDD (If that is the problem).