Iphone 5S/5 BLACK SCREEN iphone possible solution – experts what you say

I have two iphone 5 both have black screen, the light is working, pc recognises the phone. I found the same problem on a iphone 5s. no solution that i know.

Now im working on a 5s, I Reheated the pcb near lcd/touch connectors, the screen was back alive for 2 seconds, than dead again