On my old Denon 2802 there was a section called "resetting the microprocessors" or something very similar. Look for that in the index. I assume it won't come on? Mine got a surge and went out but this reset brought it back to working order.
Hi, the Denon AVR-1905 is reset by holding down the Speaker A & Speaker B buttons while powering it on. It differs from model to model, so check your manual, there should be a section there telling you what to do. If you don't have your manual, you might be able to download it from Denon USA website.