Just a note for the record that on 2 occassion the Navigation/Entertainment screen has died on me. The dash portion has always worked. Both times the second screen reactivated on its own accord after several restarts of the car and a couple hours had passed. My dealership noted no error codes and performed a software update of the head unit. They are hopeful but unsure if it will solve the issue.
At least you got a picture of the issue, so hard to deny from the dealer/repair perspective. Hopefully the software update works. Edit: did you try to reset the screen- hard or soft Note: it would have to be a hard reset if screen is black