[thatmariolover]

I'd replace the CMOS battery first off. Though there is a rudimentary way of checking if that's the problem before doing so.

I assume you're on some sort of Windows OS, which one? 98 and ME had a problem I think if it's an older PC. If not, it's probably the battery. Regardless, try this:

1. Open a DOS box (windows key-r, type 'cmd', hit enter).
2. When the box opens type 'time' and hit enter.
3. Check if there's any difference between the DOS time and the time in your Windows system tray.

If there's a discrepancy, you know for sure your battery needs replacing. If there's no difference, there's still a good chance your battery needs replacing.