Hate to be the douche that asks these questions, but I don't know you or your level of skill so sorry:

Have you checked all the cords?

Are your speakers plugged in?

Are your speakers turned on?

Is your volume turned down on the speakers?

Is your volume Muted on your speakers?

Is your volume turned down in your computer?

Is your volume Muted in your computer?

Have you tried a different set of speakers or headphones to see if yours went out somehow?

Again, sorry bout the uber easy questions, but again, I don't know you so it's best to point out the obvious and work from there.

-Twilight Storm

Is there an in-game sound adjustment that got messed with somehow?  (In Sins it would be in the menu during a game, I'd go check it out but my laptop is kaput right now and this comp is too slow to run the game, so it isn't on here.)

-Twilight Storm