This happens to me once in a while and I can't explain it either. To get your sound back, unplug the 990 or hit the main power button.

Including me, you are third person to post this over the past few months. I did report it to Outlaw and their solution was to update the software again. I did and didn't have a problem for a long time. But it eventually happenned again--when my son accidentally hit something on the remote. I have never been able to duplicate the problem--it always happens when something gets hit on the remote.