I'm really not sure why you felt the need to tell me you had two computer science degrees though.
Just exactly what I thought, when I read what he said about that, i was like .... what the?
Anwyay, again what Leeky said, its mostly driver related, but its not only in that case, sometime the plugs on motherboard has broken connection from the solder points when you unplug and plug in the jacks in there way too much, very same situation for integrated video on motherboard if you gotta bring in your lan machine from home to party back and forth often.
1. Driver related - Try and get the most updated drivers by searching the Google. E.g. SoundMax 5.1.24.2502 for a specific product, you gotta look it up to make sure it is compatible with your pc; and then try and search for updated revision of the driver.
2. Hardware related - Again what Leeky said, its mostly driver related, but its not only in that case, sometime the plugs on motherboard has broken connection from the solder points when you unplug and plug in the jacks in there way too much, very same situation for integrated video on motherboard if you gotta bring in your lan machine from home to party back and forth often, and when the video port get too loosey, you end up buying the new video card, or probably new motherboard.
3. Software related - I'm not sure if this is in the case, but did you actually updated your DirectX? There's latest redist for XP on Microsoft Download site.
4. BIOS related - Its a rare case that the battery loses their last charge and accidentally reset the BIOS back to default, hence the audio settings in there.
Good luck man