Neither camera working after iPhone 6 screen replacement

After replacing my screen (iPhone 6) neither of my cameras are working (along with the LED flash). When I open the camera app, a black screen appears. I have checked that all ribbon cables are intact (both front and rear camera) and nothing seems to be out of order.

Also, I haven’t upgraded to ios 9 for personal reasons. Im running ios 8.4.

I have tried using the camera app which by default opens the rear camera view and other apps like facetime and snapchat which by default open the front facing camera.

The proximity sensor works on the front of the phone (sometimes). it worked well before but it may be slightly out of place.