Did you isolate the battery before disconnecting and re-connecting the display assembly, as seen here in steps 29-30 of this [guide|96439|guide|stepid=136115]?
Failure to do this exposes the LCD and or backlight circuit to short circuits. This would then be a logic board issue and the usual test would be to plug the original screen back. In this case, both your screens suffer from the same problem so you most likely have a logic board failure. Look around the connectors to see if there is a damaged or burnt component. This will require a micro-soldering repair and is not DIY.