Either the cable from the display to the compressor unit is faulty or the computer in the compressor unit will not boot. Try reseating the connectors at both ends of the control cable. Otherwise, you need to investigate the computer control module in the compressor unit. It’s the printed circuit board in a white metal box.
Before removing and reseating the cable, I’d remove all power from the thing, not just turn it off.
You may get lucky, it may just be a “glitch” some stray electron went where it wasn’t supposed to?
How many computer controlled things have you turned off and on, to have them work?
When mine did that it seemed to be the temp sensor connection. Or it was the 'daughterboard' with the relay to switch the compressor on and off. On mine that had a weak power connection which I resoldered during trouble shooting. I don't get "--" anymore.