1. Make sure you have the right to share your Webcam. Ask the presenter in the chat.
2. Have you clicked the Webcam button to share? Are you muted?
3. Are your Webcam's settings correct? Have you selected the correct Webcam to share?
4. Is there another program that may be using your Webcam? Like Skype or Hangouts? Close those programs and restart your conference room.
5. If all else fails, restart your web browser and then your computer.