JVC CH-X500 CD Multichanger has power but wont play, why?

I have installed a JVC KS-FX202 head unit with a JVC CH-X500 CD multichanger. I have the correct Adapter cable fitted between the two. On initial fit the head unit works fine, but the CD only had sound from the left speakers. We unplugged and replugged the power cable and now the CD player has power but will not play when selected on the head unit??? As if the head unit does not know the CD player is installed, there is no message on the screen showing any faults, it just stays on radio! Your assistance would be most appreciated, thanks.....