iPhone SE completely dead

My iPhone SE has gone completely dead. The display is unresponsive, my computer registers nothing when it's plugged in, and DFU mode didn't help. This happened during a battery replacement, where the phone began to boot before I was ready to put the screen back on. I turned it off, finished screwing everything in, put the display on, and found the phone unresponsive. The battery had charge, and the screen was working. My best guess is a combination of the upper wiring harness going out, and me turning the phone off having caused the need for DFU mode. The flash wasn't turning on before the battery repair, and so I figure the power button must have also died at some point when I was screwing everything in, along with turning the phone back off maybe somehow messing up the OS. However a new harness is going to take a while to ship, so in the meantime, any other ideas?

Also, before writing I did a full disassembly, and at least by my visual inspection everything looked fine.