I am going to say this to anybody who will listen, with no apologies for shouting - DO NOT BUY DENON HARDWARE! JUST DO NOT TRUST THIS BRAND!
If there was a time in which Denon equipment was aspirational, or reliable, that time has long since passed.
My Denon 2807 has exactly the same problem and, I can assure you, it is a failure of the HDMI board. I can also tell you that the board only failed, when I connected my Denon amp to my Denon 2910 DVD player! It worked before, and has never worked since.
I have a number of input and output sources against which I can test. My Infocus projector can even return make/model information from connected sources but, it no longer finds my Denon amp to be a connected source.
I should point out that I have another Denon lump, hanging around, upstairs. It suffers from the power safety-shutdown issue, that Denon like to sprinkle throughout its manufactured equipment.
I can also point out that Denon are in favour of breaking and not supporting their hardware. Did you know that HDMI 1.3 to 1.4 is just a software issue, and not a reason to buy a whole new amplifier? Can you imagine buying a 1.4 Denon amp, only to find that the same, ropey software means that your amp is living on borrowed time?!
I have nothing but contempt for Denon now, and would NEVER buy into them, ever again.
Until somebody tells me different, I am hunting a Marantz SR - I like the kit, and I don't hear the same levels of dissatisfaction from their customer base.
If you're still reading, I have previously been advised by Denon that a firmware update will restart the failed HDMI board. My only problem is that, I have never been able to get the RS232 interface to work. And that is against two Denon amps!
Denon sucks, and the hard lesson to learn, is owning their junk before coming to the realisation. Denon sucks!