Check the VIDEO/HDMI menu on the on screen Setup Menu and make sure the unit is set to AMP MODE. If the unit has been set to TV MODE, this setting will Mute all audio output from the receiver and instead routes the sound out the HDMI output to be played through your TV speakers.

If this is a separates system with a Rotel processor and power amplifier, also make sure the 12V trigger switch on the Rotel amplifier is in the OFF position and verify all cables/connections between the processor and amplifier are correct.