It's rare for an audio chipset to fail. I would check windows control panel for conflicts or device drivers that didn't install properly. Uninstall any devices with a mark next to them. After rebooting, have the driver cd (from the motherboard) or vista or windows 7 dvd's ready to find the drivers if needed.
i was repairing this machine and it failed to install the audio drivers.i later found that the problem is with the audio chipsets on the motherboard not functioning.how do i repair them?
Make sure on-board audio is enabled in bios.
With my last system both the on board audio and Ethernet failed, the motherboard was fine however it was actually a bad power supply. I have never heard of anyone else having the same issue, might not even be worth checking.