Display Dead, But Radio button works, Other side of buttons dont work

[Addy25]

Hi Folks,

I've dont numerous searches but have yet to find a similar case. Her eis the problem.

Intermittantly, The Nav screen goes blank. The Radio button on the NAV Display works, and the CD thats in there works. BUT Cant Eject CD, Cant get the monitor to turn on and display what its doing, seems all buttons responsible for communication to MK4 dont work however the radio power button and channel buttons work.

Now, the car has NO video module and the screen goes completely dark, No White lines etc!!

Tried different MK4 (known working because they both work in another car)

The car is a 740i sport, came with factory NAV.

Have not played around with the fuses, or relays yet.

FINAL NOTE:

There was an error message on the screen, something to the effect of The monitor has turned off due to heat issue! very wierd as it came up just once!

Any help would be greatly appreciated!