I notice that HP doesn't offer a sound driver for that model from their downloads section, and other sources of the web seem to disagree whether the AC97 codec chip on that board is a Realtek ALC202 or Analog Devices AD1886. Which driver did you try?
The Realtek driver is available
here. The AD1886 driver seems to be harder to find (and also less likely), so I decided to not bother looking for it until you try the Realtek one. Let us know how that works out.
