After replacing Back camera, it wont turn on. why?

i recently was changing the front assembly and in doing so i messed up the volume flex cable and the rear camera cable. i then bought a replacement for the and i installed the camera and test the ipod (not being completely reassembled) and the camera app wont open the shutters for the rear camera but the front facing camera works just fine.

Why is this and what can be done to fix it