The more and more I read what you said, the less it seems graphics related. Computers are strange things... (Ive had things that have looked like a faulty hard drive or cable, but turned out to be memory).
http://www.pcadvisor.co.uk/
Ask on the forums there. There are loads of very intelligent people on there. Im sure one of them would be able to solve your problem with ease.
I have asked many questions on there, all of which have been answered by someone sooner or later. You never know, someone might have experienced the same problem already, and know the exact cure.