I'll try and waggle a few of the cables around... Do you think a new CPU and MOBO would help as it is nearly time for an upgrade anyway...
i'm sorry for the bad news, but this sounds like a virus that i have recently been reading about. the symptoms are just as you said, and the virus is not yet blockable by any virus protection yet made. my best advice? delete EVERYTHING if the problem does not go away with any normal tries to fix it. then reinstall windows (if you have the cd of course, ) and start over