Solar,
what are you using for sound,headset or speakers or both and are they selected where skuzzy says?
Are you sure you plugged into the proper output?
Oh,did you install an old settings folder in a new install? Now I'm really grasping at straws...
I had issues with sound when I went to vista so I know it can be frustrating,most my issues were solved by plugging headset into the rear inputs as the front inputs were hit and miss for some reason.