Does the light on the front of the DUET receiver light up?
If not, I would venture to guess the power supply might not be working. You can check the power supply if you have a multimeter. The center connection is + ,the sleeve is -. You should be able to measure 9 volts DC.
If the PS is not working, a better sounding replacement PS is available from Parts Express.
Linear Power SupplyIt will need a cable from the PS to the appropriate connector to fit the DUET receiver.