What is the soundcard? Is it onboard or is it a card? Is this a new card ... did you have on-board sound before? Have you checked to see if the card will work under NT? Did it work before? Have there been any major changes to the system recently? Do you run a virus scan on a regular basis?
I would start by running a virus scan. Then check to see if the card will work under NT. If you have onboard sound, you need to disable it before installing the new card (if any). I would also check both windows update and the soundcard manufacturer's website for updated drivers specifically for win NT. If is is a card, also check for motherboard driver updates along with any BIOS updates (these should also be done if it is onboard sound).
Hope this helps.
-Dave