My CDA-9813 powers up and goes through all of the modes normally (CD, radio, Aux), but it does not output any sound. Nothing has changed as I have had it for 5+ years and it worked fine every day until now.
(I have noticed that the cooling fan in the back does not move when powered on, but this may be controlled by a thermostat?!)
I have also heard (rumor) that the stereo has a fail safe that when a speaker goes, it shuts itself down.
I do know that my right passenger speaker is going out.