Great. Thanks for taking the trouble to write.
I finally managed to track down someone at B&O (customer service is closed over the weekends!) and they said that there must have been a power cut overnight. After a power cut, apparently, you get the "Wait" message for around 3 hours, after which you need your PIN code (distinct from the child protection PIN code explained in the manual) to be able to use the screen again. Amazingly, none of this is made clear in the handbook. Anyway, it's all up and running again and looks excellent.
Happy New Year to you.