iPhone 6 - What can cause the front camera, rear camera and the flash to stop working, all at the same time?
There is a power supply chip responsible for powering both cameras if you removed the display you may have accidentally have damaged this small and delicate chip, without power to the cameras the flashlight will also not work. You can see the chip pointed out by a pair of tweezers in the picture below. it is normally covered in the black substance like the parts around it, I removed it in order to give a clearer view of the chip in question.