You probably need to reinstall the Sound Card driver...
1. go to Start \ Run \ type; devmgmt.msc and in the Device Manager, under Sound, Video and Game devices, find the Audio device driver and select it with a right mouse click, and then Uninstall.. confirm to uninstall, and restart the computer and check the Control Panel\ Sound Device Properties..
2. if nothing has changed, go again to the device manager and right click \ Update the driver. Then on the Wizard select Not for the moment, then Next, and check on the line that reads Automatically install the software (recommended) and click next.
3. If that doesn't fix it. Start again the Wizard and selecting the bottom line each time (3 times), you will reach the list of compatible hardware, select a different sound card driver from the compatible drivers list* (the presently installed driver should be highlighted) and then click Next to automatically install another compatible and signed driver.. if a message box pops-up giving a warning, just ignore it.. if the driver is signed as indicated by a green check mark, it shouldn't cause trouble. *A check mark on "Show compatible hardware drivers" indicates compatible drivers, uncheck to see other uncompatible drivers.
4. Another option would be to visit your Motherboard's webpage and see if an audio driver update is available.
5. And finally a driver update utility should take care of any driver issue. And if even that doesn't fix the problem you will know it's time for a new Sound-Card