Vista - Volume slider automatically adjusts to ZERO!

This has got to be the wieredest problem I have ever heard of.

I did a clean install of vista home basic and everything is fine but I have
one really odd problem with the sound volume.

The sound slider is automatically set to zero, and the only way that I can
hear sound is by moving the volume slider up and holding it in place. If I
let go of the slider (release the mouse button), the volume immediately
slides all the way back down to zero by itself.!?

So wierd. I don't think it is driver related as I have tried updating,
reinstalling windows drivers and motherboard drivers for the sound. No
matter the driver, the problem with the sound remaining at zero unless
manually raised and held in place persists.

MS tech support couldn't figgure it out after a few hours on the phone even.

Has anyone else ever even heard of this kind of problem?