Speakers have no sound

Under Vista OS, sometimes the speakers suddenly have no sound.
One possibility is ….. follow the steps to verify:
1) Open the windows media player
2) Click “Now Playing” and click “devices”
3) Select “speakers” and click “Properties”
4) Click “advance”
5) Ensure the check (tick) is on “Speakers” and not on the “Digital output”
6) Click “OK” this normally will solve the problem