'Camera not found' after home repair.

So, problem 1: I dropped my phone, and the rear camera started buzzing loudly. Someone here said that replacing their camera themself fixed the problem, so I decided to.

I open my phone, replace the camera with a spare off ebay, put it back together and open the camera. I get a 'camera is not found' error, and other apps report that they can't detect a camera.

I assume the part is a dud, so I take it out and put back the original. Still getting the error.

I assume I've ballsed something up in my fix. Has anyone else replaced a camera and had similar issues? Does anyone know what I may have done and can possibly undo?

Thanks very much.