I can tell you the Win95/98 solution....
You would go into Add/Remove programs.... Go into Windows setup.... go into multimedia, uncheck the Audio and Video Compression (or Codec, or something, I forgot). Apply. Reboot. Recheck the Audio and Video Boxes, Apply, Reboot, and it would most likely be fixed.
Problem with WinXP..... Audio and Video Compression, isn't on the list. I'm sure the fix is still the same, but....I don't know of any way to tell windows that you want to reinstall those certain components.
Maybe removing the audio codecs from Multimedia in ControlPanel, is the way to do it.... But I don't know. I'm guessing. And I don't know what would happen if you did that.