The onboard audio is probably dead. I say use this to introduce yourself (and your ears) to a discreet sound card. The change in audio quality and clarity will blow you away and you will not ever want to go back to onboard again.
People saying there is no difference in sound quality from a sound card vs onbard are prob using 20 dollar Wal - Mart speakers / headphones or have never used a good sound card / headphones combo.
Edit: This may also be a long shot, but...check to see if your speakers are plugged in / turned on and it's not muted.