If you can still hear messages coming in then it sounds like you need a new lcd. I have fixed a few S4's with the same symptoms. I did run across 1 S4 that was dropped hard enough that the LCD cable inside came disconnected. I re-attached the cable and everything was fine even the LCD was not cracked. Funny enough a couple days later I ran into the same thing on an Iphone 4, loose/disconnected cable.

Make sure you get your spudger between the glass and the digitizer. It is very easy to get between the digitizer and LCD. AND WORK SLOWLY!!!! PATIENCE!!!!