The clock is probably in sync with an atomic clock (if you have a newer version of windows, it's probably syncing the time on you PC to the time online), thats probably why it appears a different time.
Also- make sure that your CMOS battery is OK. It may need replacing.
universe man, universe man. size of the entire universe man. usuually kind to smaller men. universe man, he's got a watch with a minute hand; a millenium hand; and an eon hand. when they meet it's happy land. powerful man, universe man.