I tried to replicate the problem you are experiencing, as you describe it.
Two possibilities resulted:
1. The PC volume control may be turned down. Try turning your Mediaplayer or remote volume control all the way down and then bring it up slowly.
2. Using the Beo 4, shut it off, and then check that your BS 4 has selected N.MUSIC OR N. RADIO. Scroll the appropriate selection on the Beo 4 and press GO, bringing the volume up slowly.