What did your dad do? If he's the type who thinks he knows everything about computers but doesn't have a clue, best keep him away. No offence to any dads, not all dads are like that, but I've seen things like this happen before.
Try reinstalling your sound card drivers first. You might want to remove the existing ones first so you have a clean start.
Try reinstalling DirectX.
Press control alt delete and look at the currently running programs. Could any of these be using your sound?