mmi not workin
 

hi im new to this, my 2007 q7"s mmi lights up only when on off button is pushed. ive replaced the mmi circuit control panel and the sterio processor, had the car to the dealer twice and still no fix.
the dealer installed the fiber optic loop and the mmi screen didn't come on. before I spend thousands trying to get the sterio to operate is there any suggestions please.

switch the whole head unit. that sounds like the issue