I have a 2005 Audi a6 and the mmi screen does not work but everything else does, centre console lights, radio, media etc. I have replaced the screen and it still does not work at all.

At the risk of stating the obvious, but could it be possible that the replacement screen is faulty? Especially if it is a second hand one? I know this does not happen very often, but maybe it is as simple as that. I have once bought a reconditioned part and it was faulty (although it was then replaced by the shop without any hassle). I'm sure it has happen to others as well. Other option could be the faulty screen on/off button perhaps? Not much help, I know. 

Believe it or not I actually haven’t thought of that, I’ve tried almost everything else but that. Thanks for the input 

I bought another replace screen that definitely works but it still had the same probably and I’m not sure what else to do?