You may want to try an older version of the driver for your audio card. If your PC has the embedded Realtek Hi-Definition Audio controller, the most recent drivers (2009) do not work with Windows Media Center on 64-bit Vista. You get the "audio device not detected" error. (and maybe other OSs too) I downgraded the driver to version 126.96.36.19948. To check the type of card and version, go into Control Panel -> Device Manager (or Control Panel -> System -> Device Manager), click Sound and Video Controllers, and click the audio card.