Power off cd changer displays off and does not work

I would inspect the harness to your unit and see if any wires are not connected..A fully connected harness ensures all functions are working as intended and if any wire that is supposed to be hooked up and isn't then there would be your issue..

Did you check the fuses? Maybe one is blown.

get a new one problem solved

try disconnecting the changer for a few hours and see if it will reset itself.

CD ERROR DISPLAYS
CD Changers
E01:
The disc magazine is not inserted in the cd changer
E02:
No disc is inserted in the disc magazine
E04:
The disc is dirty, or the disc is inserted into the disc magazine
upside down
E99 RESET PROCEDURE:
Remove CD magazine by pressing eject button on changer.
Remove all discs from magazine and re-load empty magazine into
changer. Using the Radio RESET CD system by pressing and
holding the “ON”/”POWER” button for about ten seconds, or in
earlier models the “EJECT/6” button.


FM/RF Remote Controls
E99 RESET PROCEDURE FOR REMOTES:
Remove disc magazine from changer by pressing eject button.
Remove all discs from magazine and re-load empty magazine into
changer. Press RESET button on interface unit
WAIT:
The temperature is exceeding more than 55c(130f) and the cd
changer cannot be operated. When the cd changer cools off, this
wait disappears. When the RESET button on the interface unit is
pressed, this WAIT appears for a few seconds


IF THESE ERROR CODES STILL KEEP APPEARING
CONTACT YOUR DEALER.

This system is very complicated and unfortunatly you need a scan tool and a d2b ring tester unless you are very familiar with the fibre optic ring set up for this vehicle. most likley your c.d. player is defective-is their also a phone and do you have sound from the speakers when operating normal radio function

Check the changer and see if cds are inserted correctly or if 2 cds are in one slot.

Make sure the ground connection has not been corroded or disconnected.

IT MAY HELP IF YOU CAN REMOVE THE CD PLAYER AND THE POWER LEAD THEN REMOVE THE CD'S FROM IT (WITHOUT FORCING THEM) AND THEN RECONNECT THE POWER

first try to get another display, maybe it's broken (could be the cable cutted), the changer with a motor noise in the moment you plug it, tell me that its ok (95%).