in addition to the above,
1.Make sure you have powered speakers or headphones and that you plug your speakers into the correct ports on the PC. Passive speakers (speakers without a power source) will not work well on PCs running Vista.
2.Check all volume and mute settings because there is more than one volume control. Start by making sure the volume knob on the monitor or speakers is turned up, and then set the volume in Windows.
3.Make sure the speakers or connection you want to use are selected as the "default" playback device in the Windows Sound Properties.
4.Check Device Manager to see if your sound device is enabled and working properly. Re-enable the device as necessary and update the driver while still in Device Manager.
5.Use HP Application Recovery to re-install the original driver that came with the PC and was designed for your hardware.
6.Use HP Hardware Diagnostic Tools to test the hardware and software for failures.