iPhone se 2016 won't turn on

One of the dangers of connecting and disconnecting a phone with an LCD display with the battery still connected is that it's all too easy for some of the pins to short together and blow the circuit on the screen controlling the backlight. That's why the first step in virtually all iPhone repairs is to disconnect the battery.

If you had unplugged the battery before removing the screen, it wouldn't have mattered if the phone had been on or not; that would have been a better choice.

However, that's all beside the point now; what we're trying to do is get you going again. As @ezzgen said, we want to know if the phone is dead or perhaps it's just that the screen isn't responding. There are a few things to check.

• Press the power button to turn the phone on. Is there any noise or vibration coming from it the way it normally would when it powers on?
• Connect it to a computer. If the computer recognizes it and tries to connect, then the phone is definitely alive at least to a certain extent.
• Try the silent/ring switch; do you get a vibration when you toggle it?
• In a darkened room, take a flashlight and press it up against the screen. Can you make out any image at all? If so, that would indicate a damaged backlight.

If you get any positive results from trying the things I listed above, then it sounds like your next step should probably be to consider replacing the screen. Fortunately, for an older iPhone like yours the price of LCD screens has dropped hugely; you should easily be able to find a replacement for under $20 USD, if not less.

Let us know what you find and we'll see if we can figure out what to do next for you.