Click Start, then Run, then type services.msc. Hopefully it'll come up. Check the Windows Audio service to make sure it's running. If it's not, try to start it, it may not even start.
If you can't get that far, restart the computer in safe mode and run one of those virus scanners. If you're on XP, I recommend disabling system restore at this point as well. Speaking of that, if you haven't tried rolling back to before the problem, you might want to try that too.