Pull the lid off, make sure that gray cable is plugged into the VU behind the Naza, it is possible it came loose in transit or in a crash.
Ok, it still has a VU, the VU is the LED at the front or back? The grey cable is a USB ext cable and it plugs into the VU.... see this picture.
Here is what I would do, to see if the gray cable (The one crossing the Naza) is the culprit remove the top of the unit (warranty) if any will probably be void from this point on. Pull the gray cable out of the VU and plug a USB cable direct into it, it is a standard mini USB plug on the VU. Now power up and see if it works, it could just be a loose USB cable, so try this first.