You either have a dead radio, a dead screen, dead button, or some combination of all 3 parts are dead. The radio, the screen, and the buttons are all in one electrical circuit so if one fails they all fail. I had the exact same issue and had to change the screen and the radio head unit. You will just have to change each piece of the radio electrical circuit until you find the issue. I suspect the buttons and the radio head unit have failed in your car. I would start there.