sounds to me like its not getting any turn on signal from the car if you tried another unit. on my park avenues the c&f light up just before it powers on. if this was not the case, and it worked apart from the screen i would be looking at the resistors. every car with this particular climate control unit i have seen eventually has to have the resistors re soldered back onto the board because GM cold soldered them and they break off of the board.
the resistors that break off in question are the 4 in my picture below.
6000k headlights, LED license plate fog lights, tinted taillights and to top it all off, 2 12" air horns!
the gf:'00impy 3.8, every option. COTM July 2013