That’s a very thorough explanation of your steps and you did everything “right” from a repair perspective. Here are a few suggestions and observations:
* If the phone had no shield holding the screen connectors, that means it was repaired before (by whom?). There may be some history there, like overtightened screws. Sometimes issues stay latent for a long time and only resurface after a strong impact or subsequent repair.
* While the typical screen repair related issue is a blown backlight filter, sometimes it’s the LCD driver that gets blown. However, you do say that the battery was disconnected first. Was it also the last thing connected after the screen replacement?
* Did you check for any pry damage around the battery connector? Accidentally prying FL2400 (see image below) can cause the symptoms you are seeing .
* It could also be that the screen was damaged when you lifted it off. Considering it was previously repaired, it may have been a lower quality screen.
* You can use a [https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=USB+Ammeter|USB Ammeter] to determine if the phone is really drawing current when it should be charging.
* Try connecting the battery but without the screen. Then connect it to an iTunes enabled computer. Does it get recognized? If yes, then the phone is alive and you have some display/driver related issue. If it isn’t, then you likely have a logic board issue.
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