Screen won't turn on but iTunes recognizes the phone

Originally phone was dropped and landed on the power button which is now hard to press. But did a tear down and checked all the connections. After reassembly, when plugged in iTunes recognizes the phone, but the display is completely black. Any ideas on why the phone would be recognized, but no screen?

Checked all the connections. All were tightly seated. Now iTunes won't recognize phone at all, which I assume means the phone is not turning on. May have to take it to a repair shop as it seems there is more going on than just the LCD screen.