Black screen after minor shock, power button doesn't seem to turn off

Hi All,

Just posting here in one last attempt to get this thing working without buying a new display assembly.

My brother used his phone to playfully hit a friend (who was acting dumb) on the stomach. The amount of force the phone supposedly received was probably about the same as dropping it a couple feet onto a carpeted floor. However, after this incident the LCD stopped working. It still played sounds and the capacitive touch buttons still lit up when pressed.

At first I thought it was the motherboard, since it was a refurb I had just installed to replace one damaged by rain. I sent the refurb back and bought a new one, but the problem persisted.

I've visually inspected the cables as best I can, and they seem to be fine. I don't believe the digitizer is working, since the capacitive touch buttons don't light up when you touch the screen (they're supposed to, right?). Also, when I press the power button it doesn't disable the capacitive touch buttons, which makes me think it's not shutting off (which is why I originally thought it was a motherboard problem).

It seems odd that a light tap, something much less forceful than a drop on a hard surface (even in a case), would have ruined the screen, but maybe it did. Or maybe there was some water that was in the screen and the knock moved it into a critical area.

Anybody have any ideas as to what to try before buying a new display assembly?

Thanks