how old is your soundcard? These things do stop working' unfortunately. Mine did
As Dave said;
Check your sound card, this is inside your computer and should be the card that has the pink, green and blue circle ports in it. If they aent colour coded, it should have something to tell you that its where your speakers plug into

.
Download the latest Media Player, which is version 10 I believe. it can be found in on the Microsoft website.
If that doesnt work, try different speakers, headphones etc.
if that STILL doesnt work, I'd just assume your sound card broke and get a new one, :S. Unless someone else has any ideas.
