Chosen Solution
I replaced the battery in my iPhone 6S and also the home button, which had first stopped accepting fingerprints and then stopped working as a button entirely. I’ve put it all back together and it’s not turning on, even after charging for an hour or so. It does do the two-short-vibrates when you plug the cable in though, so something must still be alive? I’ve tried a hard reset (home and power buttons for ten seconds) but it didn’t work. Any ideas?
Did you have the battery disconnected before removing and replacing the screen? It sounds like you have damaged the backlight circuit. See if your PC recognises it and shine a torch on the screen to see if there is an image there. This is one model of the iPhone that you cannot disconnect the screen without disconnecting the battery. If it is the backlight you will need to rule out a faulty screen before moving on to the logic board but unless you have the equipment and knowhow of microsoldering it might be time for an upgrade as this repair could be worth as much as the phone.
