Underneath 'Program', Press Step, then Clear. Repeat until 'No Input' is displayed on the panel.
It sounds more like a technical fault though with the amplifiers bias voltage. See if the fins at the rear of the unit get hot quickly once turned on. If so, there are a couple of potentiometers that need changing and resetting inside of the unit. This is a common problem with the Beomaster 5000, and easy to fix.
Cheers
Ben