disapearing files and date change

I have an unusual problem with a pc running windows xp pro. The machine exhibits some strange symptoms even after a clean install. The date changes to a random year in the 2020-2030 range. The files in the outlook express inbox disappear - not the inbox itself and the files on the bakup partition disappear completely.
The machines is 6 months old and up till now has worked fine.
Specs are:
Asrock motherboard
AM2 quad processor
2GB Ram
320GB hard drive
8800 series geforce video card.

The memory tests clean as does the hard drive.

Help!