Q5 MMI Failure ?? No power ??

Hi Guys and Gals,

New to the Forum, but i cant figure this problem out im hoping one of you guys can, or know someone who can.

Started a couple of months back, started the car up and the MMi screen did not work. Stopped car and left it 15 mins started it up again and all was ok, for approximately 3 weeks. Then it just totally failed. No power to The central control unit, no screen nothing no sound (apart from parking sensors). so did some research and it might of been the battery (been 4.5 years old) so i checked the voltage and was 12.2 volts output, which is low, so bought a £200 S/S battery and still no joy.

So got a diagnostic check carried out. all he could find was AUDIO - NOT ACTIVE, thats it no fault codes, no blown fuses, HIGH and LOW CAN all ok, carried out a communications test on the fibre network and still nothing  to find. So he said he thought it could be a center controls fault. Managed to sourse one from ebay (same model and part number exactly). % mins to change over with ignition off. Put new one in and no joy again. This time the new unit places a parking brake fault on the dash. Took out key and replaced with old unit, parking brake fault dissapeared but still no power to anything. Person i bought the control unit from said it will be the head unit (the actual part where your DVD is ) im pretty lost 

So any hel would be great.

Regards 

Paul