Chosen Solution
I had a customer bring in a 5s today that she said needed a new battery because it wouldn’t charge. There was no visible damage to the phone or screen, so I assumed it was either the battery or the charging port, I replaced the battery, but the phone still didn’t turn on, so I tried a new screen and it worked. Then when I transferred all the components from the old screen to the new screen, it won’t turn on again. I’ve tried more screens and it won’t power on. I’m not sure where to take it from here.
I think you tested the screens without taking the battery off first. You probably destroyed the backlight line(s) on the mainboard.
Did you try to put the screen on with the battery connected? Or didnt turn the phone off or used metal pry tools? If you broke any of those above then the phone could be broken.
Try to power it up and don’t connect the proximity flex to motherboard, maybe thats why it doesn’t turn on. Or connect only the screen flex cable itself, when it powers up you know that the proximity sensor or selfie cam is faulty.
