Have you ever reset the bios or reloaded the same bios file to correct any corrupted files? The registry could also contain errors so a good registry sweeper would be good to get. You can also take your Windows disc and do a repair to see if there are any errors of corrupted files.
If you go into the action center and run the troubleshooter it may come up with a problem and a solution.
You also want to make sure that the sound card is selected as the sound playback device and anything else that has to do with sounds.