have you tried if its just the screen?
can you change settings when its in say p-mode?
To find out you could get it to green-mode, go to menu turn off the Beep, then turn to p-mode, ant then hit menu, set, turn dial press set. And when it beeps I think you could install it blind.
It's definitely not the screen, it works fine in both the auto modes, and if I take a picture in P mode, AV or whatever the picture can be viewed if I go back to either of the two auto modes.
There must be something inside the firmware that has gone aray I would assume as EOS says busy, I was shooting a continuous burst when it packed in, in raw.
It's still useable as an auto camera, but that's not how I shoot, and without display I can't set up my customs..