Computer showing wrong date in morning if left on overnight

I found a couple of threads over in hardware issues that suggested it was a a battery problem but I don't think mine is battery related. This problem happens only when I leave the PC on overnight so I usually just don't do that anymore. But last night I had to because I was dowloading an album from Amazon that was taking forever. This morning, the date is something crazy (like the year 1099; each time it's not the same year but it's centuries ago each time) and it errors everything on my system. Nothing starts up, my external hard drive can not be found and so on.

It's easy to fix - restart in safe mode, adjust the date and restart. But what is causing this? I assume a virus of some sort BUT I run Norton once a week and Norton is also on whenever the computer is on "watching" or whatever it does for viruses.

Thoughts?

Oh and we have XP.

I think you must check for Cmos Battery... I think this is the time where you require to replace the CMOS Battery.... CMOS battery is located on the motherboard which looks like the battery in your wrist watch....! I hope you will find it & replace it...!

Also Check the problem related CMOS Battery Here :

http://forums.techarena.in/portable-devices/1202101.htm
http://forums.techarena.in/operating...ms/1183281.htm
http://forums.techarena.in/operating...ms/1093722.htm
http://forums.techarena.in/tips-tweaks/995407.htm
http://forums.techarena.in/guides-tutorials/954999.htm

Sounds like you need to replace the PRAM battery. Very easy to do. Your computer's date relys on an internal battery.... this has probably died and needs replacing...

I think you bios is corrupted. Normally the time setting is saved in the bios settings. If you bios is not saving then you will need to flash it. Restart your system and enter your bios setting by pressing del or F2. Change the time and save it. If still the time is not saved then you will need to flash the bios otherwise there can be issue with windows.

It's weird though b/c the actual time stays the same, just the date screws up. I will check the bios and battery though. :)