If you've gone through all the set up checks and allowed access to your camera, but you're still not getting a preview from your camera, there are a couple of issues it could be.
The camera is connected to another program
If you have recently used another program which uses your camera, Skype or FaceTime, for example, it could be that this hasn't correctly released your camera.
The easiest way to solve this issue is to restart your computer, then log back into the interview and start the setup again.
The camera is broken or not connected
On most devices, if the camera is working a small light will come on next to the camera. If you don't see this light come on, it is likely the camera is broken or not connected.
If you're using a USB webcam, make sure it is plugged. If you have Skype of FaceTime installed, check the camera works with that. If it does, close that app and try the setup process again.