Chosen Solution
Today I got a battery and a screen replacement for my iPhone SE 1st gen and followed instructions to replace both. At the end of the procedure, before pushing the display back in I booted and everything was working fine, the new battery was at 30% and the screen, camera, proximity sensor were all working. I then shut the phone down and pushed the screen in, but it didn’t fit, it was slightly too big and one corner of the frame had a slight dent. so I used my sucker to pull the screen back out in order to fix the dent in the frame, but I pulled too hard and instead of pulling down close to the home screen I pulled at the top, this moment I think I managed to damage something, because when I fixed the dent and put the screen back in (with a lot of applied pressure, this is the other moment that I suspect I might have broken something) the phone didn’t boot anymore. I hope I only broke the wire from the screen, but the phone gives absolutely no response when I plug it in or when I try to boot it. Is there a sure way to tell what’s broken? if it’s the motherboard or the screen or whatever? I still have my old cracked screen which I could try placing back but I first would like to know if it’s really the screen or maybe something else.
The best option you have now is to put back your old screen and see if the phone will boot.
