Hey.... you've changed your avatar. Cool.
First, this is no guarantee it will work, fair chance it will, but you cannot blame me if.... Best double check an other person's opinion about this. (the following process can be undone again too). Well, no real biggy doing it, but the problem might not be solved.
Um, after some searching (been a while since I did it) and translating stuff.
Go to; start > open; all programs > open; accessories (desk-accessories) > open; system tools > open; system restore....
Pick a restore point, a date previous, a date before, the sound went dead. I'd say just before and not a year back for instance. (> next)
Good luck.