Well you could run chkdsk (XP) if you think that it's a bad sector. Seriously though unless you're running under extreme conditions you let your cooling system go to pot or the drive is old it's not as likely as a software problem. another thing that can cause strange problems is if the cmos battery goes out. you should replace those every year or two.Crazydawg had a powersource go out which as you might imagine could cause any type of symptoms but again if the power supply is not overloaded, overheated, overused or otherwise abused - not too likely.