Audio not working...

I was playing Starcraft on bnet today and I'm in a game when suddenly the sound goes off. At first I thought I accidentally muted the sound options with a ctrl+ but when I checked the audio settings they were normal.

I exited starcraft to find that none of my sound was working. I checked sound settings and all was normal. Nothing muted. I even rebooted my computer and it didn't work.
Then I ran DirectX Diagnostics and tested the sound...no results there. I also set it to No Acceleration...no results again.

I have a feeling this is a problem with my sound card. I think it's happened before too. I'd be grateful for solutions.

Thanks.

Make sure that everything is plugged in correctly, you may have moved something & the speaker lead may have come out. You could try re-installing the sound drivers.
What sort of sound card do you have? is it on-board or PCI?

Try plugging in a pair of headphones. If there's sound, yuo need new speakers. If not, then try reinstalling the drivers. If all else fails, you might need a new sound card.