Chosen Solution
I was changing my phone screen cause I cracked my old one so I shut down my phone and took off the screen and detached it from the mother board. Soon after I was moving my phone and I think I may have held down the power button and turned it on. Will this cause damage to the phone in any way? If so what will it do?
In normal circumstances nothing wrong happens if you turn it on without your screen plugged in, but avoid working on the phone while it’s turned on, you may incidentally short something. Gently unplug the battery connector before doing anything else, install your screen and before closing up the phone reattach the battery. That would minimize possible damages.