Could be a virus ... I would update your virus definitions and try to rescan.
It's probably a long shot, but you may also want to try installing a firewall just in case. You can download ZoneAlarm for free at
http://www.zonelabs.com/store/content/comp...kulist_download
If all that fails, your hard drive may be shot, have you had it for a long time? If so, it may be time for a new one.
That's about all I can think of. Hopefully it will help.