Mixer device/driver uninstalling automatically after bootup

[forlorn]

So my dads computer works fine for a couple of months and suddenly decides to start uninstalling the windows sound device (the error reads that the mixer device is missing). This happens a couple of minutes after bootup, that means for a couple of minutes right at startup the sound works. And if you turn on music or any other constant sound it doesnt go away, presumably because the sound driver files are in use..?

Now its driving me mad, because I have no idea what it is, Ive scanned the computer for viruses and spyware finding nothing.

The sound card is the standard ac97 thats on the mobo. I've tried reinstalling the drivers that came with the MB and the latest ac97 drivers with no success. Its windows xp sp2 all updates applied.

Any help would be greatly appreciated!

Edited November 14, 2006 by forlorn