I'm kind of a little bit of an computer expert, so I know some things you could try:
1. See if audio works in other applications.
2. Do as Shywolf said: Go to Contol panel > Hardware and audio > Audio
and play around with the different audio devices there and see if it helps.
3. Go to Contol panel > Hardware and audio > Device manager
and see if there are any errors with your soundcard driver.
4. If you know how to do it, try reinstalling the drivers (if the soundcard is built into your motherboard and they don't use two separate drivers, you'll most likely want to reinstall the motherboard drivers). You can most likely find them at the manufacturer's website. Do NOT
use windows' automatic driver-finder and installer, because it might install the wrong driver.You can skip the following steps if audio in other applications did work, if you have a portable computer or if your computer's soundcard is built into the motherboard.
5. Check the connection between the motherboard and the soundcard inside your computer.
6. Test the soundcard in another computer and see if you can get it to work there.
I hope these tips helped you! Good luck!