I had the same problem. I tried everything and was getting sound from the headphones only. I finally went into Control Panel using the classic view and clicked on Smart Audio. If you have it, click on that and run test 1 and Test 2 from the Audio Director tab. My sound came back during the test. I then noticed in the Voice Enhancements tab that speakerphone/internet telephony was selected. I unselected it by selecting "no enhancements". My sound now works. I may have clicked on the reset button while playing around with Smart Audio. Maybe it'll work for you too. I'm no computer brain so I have no idea why it is now working.