I can’t say for certain on the iPad 5, but usually on iDevices the front camera will not work if the rear camera is not in a working state. So for now, focus you’re attention on the rear camera (you can simply disconnect the front camera).
Check the Rear Camera for any signs of damage. The flex or connectors could be damaged and that’s pretty much all it would take to cause this issue. Sometimes the RCAM gets damaged while removing the glue residue from the housing.