Suddenly Graphics Are Acting Strange

I recently brought my desktop to college via car and it was working perfectly for a couple of days. Today, it has suddenly been acting very strange. While I was casually browsing the net, the refresh rate became very slow on my screen so that all of the motion was jittery. The computer eventually froze, so I hardbooted it. When it restarted, it was stuck in 800x600 resolution instead of normal 1920x1080. Also, there were white dotted lines, that I believe are called artifacts, on the start up screen but then disappear once at the login screen. I tried to update all of the drivers and and it was still stuck... So i eventually did a system restore and took out my GPU, GT 8800 GT, and let everything cool off for a while. At that point when I put everything back, the computer booted up and it was in some resolution that was less than max like 1024 or something. I was able to switch it back to 1080. Now it works, but everything is very gittery and not smooth moving. When I drag a video it looks like the a stream of windows.

From what I have read, it seems like a problem with the drivers, GPU, or PSU. Idealy, I really do not want to have to spend any money to fix this. I don't think it is the graphics card or PSU because I had used them both for nearly a year flawlessly. Is there anyway to check specifically what the problem could be? Any advice would be greatly appreciated.

Thanks!
RS