Mr SmD PangerLenis, thank you very much. Your lordship saved my sanity. I installed the experimental DayZ, connected to a server, get out. Copy and paste the Experimental files into the DayZ folder, overwriting all files. I connected to the server but received a rejection message (bad version). I did the repair inside Steam itself, a few hundred Mb. It worked PERFECTLY.
#DayZblackscreenproblemsolved