If you have any of its sound outputs connected to a TV or tape deck do they get the signal? If so, then we know there is sound processing somewhere inside the unit but not emerging to anyplace that requires amplification.
A quick basic check would be to tune an FM station, run an RCA cable pair from the audio output for a tape deck (see the picture at the link) to an analog audio input on your TV. Select that input on the TV and you shouls hear the FM station, or anything the receiver is configured to play. If it's silent then there is no audio signal circulating in the receiver to get out to the amplifiers.
Check to make sure Multi-Channel input is not selected unless that is what you're listening to as it bypasses all other sources analog and digital EXCEPT the tape; and check any Mute or Zone Controls, too.
If you hear the program on the TV but not through any attached speakers, then the amplifiers are all disabled for some reason. The click I asked about before... when you turn it on does it get a click about 5 seconds later. That would be the protection circuitry turning OFF to allow the amplifiers to function.
I notice it has a Tape function. Make sure it isn't selected as it assumes a tape deck or processor is attached and will only play back what would be coming FROM the tape deck or processor. On my Pioneer receiver it also disables any digital signal processing.
Sometimes when I'm watching TV with the remote on the seat someone moves and something bad happens. It's always some unfamiliar button that gets touched unintentionally. Look over the remote for things like MUTE, Multi-CH, Tape.