Chosen Solution
I removed the cracked screen and replaced it with the new one. Before I seated the screen onto the bezel, I checked to make sure everything worked and it did just fine. After I installed the screen it stopped working, I removed the screen, went through the process once more, the screen worked but stopped working when I put it in place. WTF!!
My thought is the connector or ribbon cable. If the connecter is seated correctly move to the digitizer ribbon. I like to see happy cables. Nothing bent sharply or wrinkled. With the iPad turned on. You can hold the screen on its side. Dont put finger prints inside the digi screen…. While on its side carefully push on the ribbon cable. slightly adjust things and test the screen while its sideways. See if you can replicate it not working. If cables arent the problem it could be a bad digitizer. Also check to make sure nothing is touching the digitizer while its closed, a piece of glass, a screw not tight and touching back side of the screen. I have found all sorts of tiny crap that just barely touch the screen or ribbon and makes everything go crazy. Good luck. Troubleshooting iPads can aggravating because its always something simple or chasing a bad part.
Just to be clear, you replaced the actual LCD, not just the front panel/digitizer? Either way, my first thought is that something is reading as disconnected or is touching something it’s not supposed to when everything is all closed up. I would check and make sure all your connectors are firmly seated, and that all of the cables are rounded, no hard creases where lines may be broken, or traces may become exposed and contact something they aren’t supposed to and nothing is getting pinched. I know the LCD cable is basically folded in half when the device is closed so i would inspect it closely.
