I can't get sound from my denon avr 2808

I would think I have somehow turned off a channel or source button since this (to me) is a very complex receiver...any ideas as to why I can's get sound from any input channel from either a dvd/cd player or a dac running of my mac with rca's?
I have a Denon 2910 DVR.  There's an audio mode that shuts off all digital OUT and only outputs analog.  I wonder if your AVR might have a function that blocks digital IN???

Can you get sound through it from an analog source?
I don't have an analog source currently. I thought maybe I had turned the fader to the rear channels, but nope, that didn't seem to be it.