The first thing to try always is to reinstall the sound driver. To do this , go to Star. right click My computer. Click on manage and then select device manager. In the list on the right , click on the plus sign next to Sound, video and game controllers. In the list that shows up, double click on each one until you find the one that shows you a driver tab. Click the driver tab and click reinstall. And let the computer search from the internet. One the driver is reinstalled, restart the computer, everything should work fine
