Rear “back" camera isn't working

Hi...
I bought htc desire 816 dual from a year ago. Last month the rear camera isn't working. Actually it isn't recognized by phone as when I open the camera app it opens the front camera only... I tried different solution.. I tried downloading other camera apps.. Doing a hard reset.. And finally flashing the CM12 but the problem wasn't fixed... So any of you guys knows how to fix?,
Thanks in advance...

Replacing rear camera module

On rooted Developer Edition Ultra:
Is there any additional procedure needed after replacing the rear camera module? The phone has random camera busy/restart errors. Attempting to isolate apps via SafeMode was inconclusive. So, I decided to disassemble the phone and re-seat the camera ribbon cable - after reassembling, the camera works for a day or two - then the error appears for a while.

Thinking that it might be a failure of a camera component itself I replaced the module with a new one (bought from eBay) yesterday and when reassembled/rebooted - the new camera did not appear. I reinstalled the original camera which is currently working.
FYI - all ribbon cables are aligned, clips tight etc.

When I have some time I will reinstall new camera again and reflash with 4.4. Does anyone know if a new module needs to be 'initialzed'? My assumption was that installing the like component would simply 'work'.