My sound not working

go to your device manager and click on hardware, There it must show you what is wrong,
If there is a (!) sign at audio then click on it and take a look at the drivers, Maby it needs to be updated.

What did you do before the sound stopped working?

are you using the onboard sound from the motherboard or do you have a sound card ?, what make and model is your motherboard ?.

Is your computer turned on?

Post more information.