And made a reasonable suggestion.
I hate HP. I have a laptop in the dv9000 series that started breaking down by degrees when it was 10 months old. When I contacted HP for warranty support, they told me that I was out of warranty. I may or may not take the box to MicroCenter to be repaired. I bought a Mac so I have a stable and functioning computer.
Anyway- exhaust all of your support options with HP. Really push it. Don't know from what you have posted so far if there is a failure on the hardware or if this is a software issue. Check the Device Manager and see if it says that the sound card is working properly. Use the HP online troubleshooting guide as it really is quite good.
The biggest handicap I have from here is that you are likely running Vista. There have been driver issues with Vista so that may be the foundation of the problem. Check HP to see if new drivers have been made available. Unfortunately, I know very little about Vista.
At the worst, bite the bullet and take it to a tech. Look for a small independent shop. Avoid Geek Squad as a lot of their computer guys are not warranty certified techs. But start with HP.
HP bites at customer service. But their online diagnostic guides are quite good. Give it a shot.
Good luck!