PC clock problems – time keeps stopping

I recently upgraded to Windows 2000 from Win98SE and my bios has reset its speed on one or two occasions since. I now seem to have a problem with the date and time which stops or loses time even after resetting it.

I have only had the pc for a year so not sure if i need a new CMOS battery or a BIOS update?

I did read somewhere that windows 2000 does strange things to the date and time.