It does not seem to happen in safe mode. If it does, I wasn't in safe mode long enough to see if it would happen, but usually it happens in a matter of minutes. So I think it's fine in safe mode.
I tried doing a repair from the install disk, but nothing changed. Like I said, it's getting worse. Now it's triggered by pure randomness. In the beginning, as long as I kept my mouse in the desktop and not near the start menu, it would be okay and I could be on for hours. But now, it goes off whenever. I was trying to transfer files onto a different hard drive, and while I was doing that transfer, it happened. So that's how I know it's getting worse.
There is no antivirus program installed on this computer, so I guess a virus could be an explanation. However, I was using my computer before and it was perfectly fine. I turned it off and left for a week, came back, turned it on, and it immediately started doing this. I don't see how a virus could have been caught during that time, but hey! There doesn't seem to be any other possible answer.
If it is a virus, is there any way to fix it? Or will I just have to do an OS wipeout?