No Sound - Preceded by rapid input switching on its own

I have a 3 year old Denon AVR-3805 that has had low usage since I bought it. Recently, I turned it on and suddenly the inputs started switching radonmly and wildly on their own. It would say "H/P Input....." then switch to DVD, then it would say "H/P Input....." and switch to another source. Whenver it said "H/P Input....." the sound would go out. The sound would come back on briefly when it went to DBS (TV), which was the source running at the time. I turned it off and let it sit for a few days. Now, there is no sound at all. As I try to toggle through the various Surround options, only the FL and FR speakers appear in the diagram on the display. No other speakers in my 5.1 setup show up. But regardless, there is no sound either way. What does "H/P Input" indicate? I've never seen that before. Why would the unit "get gremlins" and just start widly switching inputs back and forth randomly on its own? Any thoughts on cause or possible resolution? Thanks....
Description of my setup:
I use this as a pre-amp and send speakers through a Rotel amp.
Speakers B&W 800 series (5.1 setup)
Satellite cable high def receiver from Bell Canada
Pioneer Elite DVD player
Sony CD player