Screen is black after replacement and..

So , we tried to replace the iphone screen because its very cracked. At first it turned on but looked glitchy but the touch screen didnt want to register. After that it just wouldn't turn on. We checked everything and nothing was damaged. Put the old screen back on but no dice, still nothing. I have it plugged into the computer and ive tried hard rests and dfu. Itunes recognizes the device and i'm doing a reset/ restore but it still won't turn on. Was it broken somehow while trying to switch screens? how come it worked and then suddenly worse off without doing anything?