Question about Denon AVR-X1700H DAB

Who knows what to do? The device switches off apparently because of overheating, but it worked without problems in high summer temperatures. Now the unit cannot be reset as recommended in various forums, and a factory reset does nothing either. Either it flashes red every 2 seconds or green every 2 seconds after several starts. I have also disconnected all the speakers from the unit, but to no avail. Who knows what to do?