If your camera or microphone are not activating it is usually one of two things:
1) you haven't allowed the camera or microphone in the app or
2) the video application is conflicting with another video meeting app or your VPN
You can click the little lock symbol to the left and scroll down to site settings and to the right of the word camera and microphone and ensure you have selected allow. Then reload the page and proceed.
If that doesn't solve the problem, completely restart your computer and open Chrome browser and proceed from there. Make sure your VPN has been disabled on restart if a VPN exists.