Phone not working after screen replacement

iPhone 6 screen was pretty busted and like the inside of the phone was even exposed in some areas. I got a replacement screen, did the replacement as usual. Battery disconnected , made sure i was gentle and what not. Just another day.

As i always do, before putting putting the plates back on i tested the screen by trying to turn on the phone. It gave me a dead battery indicator, so i was content and started screwing everything back in. I made sure all the screws went into the correct places and everything. Put the screen back into place and threw the pentalobes back in and plugged it into the charger to get it charged up before the customer comes back in for it. When i plugged the charger in it at this point it didnt show anything. I didnt pay attention to it figured it needed a second cause it was all the way dead. I come back to it 10 minutes later and nothing. Nothing shows on the screen. Tried hard resetting, tried taking it all back apart and reconnecting it. Nothing. Thought maybe the battery went bad. So i got a replacement battery put in. Still nothing. Even tried another new screen in case the screen was bad but still nothing.

Im at a loss. I dont know why it would turn on briefly and them not come back .

It is not recognized by my computer, no sound, put it under light to see if maybe theres a dim image but nothing.

Anyone experience this and have a fix?