What to do if audio output is not automatically routed to a Bluetooth audio device?

After upgrading the Operating System to Windows Vista Service Pack 1, when a Bluetooth audio device is connected to a Windows Vista-based computer, the audio output is not automatically routed to the Bluetooth audio device.

Please refer to the steps below to change the default sound device to Bluetooth audio device.

1. Click Start, and click Control Panel.
2. In Control Panel, click Hardware and Sound.
3. Under Sound, click Manage audio devices.
4. In the Sound box, click the Playback tab, select the Bluetooth device, click Set Default, and then click OK.
5. Restart all the multimedia programs that are currently running.

For detailed information, please refer to the website below:
https://support.microsoft.com/kb/933144/en-us