The seller said that he tested and it worked ok.
The screen is blank, but you can see the backlight coming on.
I'm going to try tomorrow another mk4 drive form a BMW M3 to try rto isolate the problem. What should I try? Should I plug my mk4 drive in his car and see if it works or take his good one and try it mine? Do I need to disconnect the neg battery before I unplug the good one out of his M3?

Thanks and let me know.