My cameras and flash don't work

I bought a phone to repair, cameras and flash didn't work. Got new screen, power flex cable and new rear camera. Everything but cameras and flash work perfect. When I switch camera on, it comes up black but with the words (video, photo, square etc) but screen doesnt change even when I try to turn it to front camera. Flashlight won't even turn on even by pressing the torch switch? I have no idea what to do next