Display froze and faded out, but still doesn't work after replacing.

I was using my SE when suddenly the display froze, developed a really strong red and purple tint, and got lines all over it. Then after about fifteen seconds it faded to black. I force shut it down but it didn't seem to turn back on. Later on I plugged it into my computer and iTunes would recognize it(but wouldn't connect because I couldn't unlock it). I talked to Apple Support for a long time and after trying to update it in recovery mode, they said that it's likely that the display broke. But my display's in very good condition, and I just swapped it out with one from another iPhone SE, and I'm still not getting any picture or backlight from it, and the display from my phone works perfectly fine on that other SE. I'm pretty sure that the phone right now is stuck in the setup menu after updating it to iOS 11.3 (which it was already in), so I can't use the mute switch or Siri or QuickTime streaming to find out if anything else is working (iTunes was being difficult about recognizing it for a while, but now it is). This is seeming to not be a display problem, right? Really hoping this is something I can fix without needing to take it into Apple or buy a new logic board or something. Thank you.