Please follow below steps to fix it first:
1. OPEN YOUR "CONTROL PANEL"...THEN OPEN "HARDWARE AND SOUND"
2. LOOK FOR AND CLICK OPEN "DEVICE MANAGER"
3. SCROLL DOWN TO '' SOUND, VIDEO AND GAME CONTROLLER''
4. RIGHT CLICK "SOUND VIDEO AND GAME OPTION"...THEN AN OPTION WILL COME UP SAYING..."SCAN FOR HARDWARE CHANGES"...CLICK IT AND HEY PRESTO...YOUR SOUNDS AND VIDEO AND EVERYTHING IS WORKING.
Start windows audio service
1) Click on Start and Run
2) Type the following command and press Enter
services.msc
3) Scroll down to Windows Audio in the right-hand column and double-click on it,
4) Make sure the Startup Type is set to Automatic and click on the Start button under Service Status.
If it does not help, maybe there is something wrong with your sound card driver. You can update it by using http://tiny.cc/o6xerx. With it, I have downloaded and updated many drivers. Hope it can also work for you. Download and install it, then it will automatically scan for your system and recommend suitable drivers for you. You can download or update drivers as you need.