First, do you have a red X on the Speaker icon in the Notification Area of the
Taskbar? If you do, then your audio adapter is not properly installed and you
need to install the proper Vista drivers.
If there is no red X and in Control Panel (Classic view) > Device Manager >
Sound, video and game controllers there are no red Xs or yellow exclamation
points for your audio adapter, then right click on the Speaker icon in the
Notification Area and select Playback Devices. In an empty area of the Playback
Devices window, right click and check both "Show Disabled Devices" and "Show
Disconnected Devices". Highlight Speakers and press the Set Default button.
Use the Properties and Configure buttons to set up your speakers. While you are
there, use the Sounds tab to test your speakers.
If you are using a SPDIF (digital) connection to your speakers, set SPDIF as the
default and enable SPDIF output in your sound card's audio manager application
software.