Doubt it's a virus based on what you said. Check control panel to see if you have any yellow exclamations. If not, you may have a serious registry problem or, as someone mentioned, may be overheating. Your PSU might be going bad also. Heck, there are a million things which might cause that sort of behavior. A windows repair install would fix a lot of problems also. I was infected once with a virus (back in my hacker days, fortunately it was on a floppy). I've also received a couple of e-mails with viruses, so they're definitely a consideration. Norton found them 2 of the 3 times (the 3rd was the "Happy Birthday" virus).