Why won't my screen work?

sounds exactly right, if you plug it into itunes and its detected then it means that the motherboard is working and that you simply have 0 display. Open the phone up and clear the ports on the motherboard for the display, make sure the gasket around those ports isnt getting caught when you seat the lcd screen ribbon cable, make sure the display port on the motherboard isnt damaged and is clear of debris. Also make sure you arent pinching the lcd ribbon cable on anything when you are closing it up.

Finally check your original screen if you still have it, i have seen sometimes on the pentalobe screw posts there are rubber boots that you need to move over to the new screen otherwise it shorts when you close it up. Hope this helps good luck!