Chosen Solution
The screen was changed out. Now the phone won’t display anything. Even if I switch back to the old display.
Is the phone recognized by iTunes? If yes, then based on what you say, I suspect that you blew the backlight circuit on the logic board. To confirm, plug your iPhone into an iTunes enabled computer and shine a bright flashlight on the screen. If you can see a dim image, then the backlight circuit is the issue. This can happen when the screen is removed with the battery still connected and would require a micro-soldering repair.
Minho, provides a great solution. And your question you asked is a good one. If the device is connected to iTunes, and iTunes says that it can’t connect to the device or can’t access it, that is because iTunes requires the device be unlocked to gain access to the phones data. But that’s only a guess because you didn’t say what the error was. I’m just assuming here. In your case the backlight like Minho said is fried and is extremely difficult to type your passcode in. Unless you now how to micro-solder, then yes your phone is toast. Remember to unplug the battery, it’s basic precautions that every guide will tell you of. Trial and error, it’s terrible. iPhone 7’s are very sensitive to a lot of stuff. And a lot of people have even had problems with the backlight going out by using the front facing flash.
