The screen and buttons usually interface with the receiver and microprocessor thru a common interface. That interface has failed or connections from the main board to the front panel have failed.
We know this because of everything that still works. Your options are to find another pitiful OEM head or to upgrade to something that does not date back to the 1990s.

Yes, you can find OEM heads on the used market, if you don't mind spending way too much for old crap.