Chosen Solution
I first replaced the screen and got a boot loop error. When I connected the old, broken screen it worked fine and booted properly, so thought it was the new screen that was faulty. I ordered another replacement screen and did the replacement but afterwards the setup just stayed on the apple logo indefinitely. I thought this screen was faulty as well so reconnected the original broken screen but the same thing was happening with that. I read through a few forums saying it may be the camera flex cable that is broken, so I disconnected that and there was no change, still staying on the apple logo. I have now bought another camera flex cable to double-check if that’s what is causing the error (I may have broken it during one of the replacements), but no success.
I had this happen on an iPhone 7 Plus that I was working on. Double Check the connections from the screen going to the motherboard. Apparently one of the connections on the screen was not seated correctly and was causing the phone not to boot.
If all the cables are connected correctly, I’d try a new front camera flex just to be sure. 7s boot loop for pretty much any little issue, just try a couple things if you have parts around
Did you disconnect the batter before repair and connect the battery last after the repair? This can happen if you have damaged the home button flex. Maybe the first screen was faulty but when transferring components to the new screen then you may have damaged it the home button flex. Another reason could be you somehow damaged the battery when repairing the screen however that isn’t very likely to happen.
