I have a feeling that your cam is either disabled or not set as default.. Please see this video to show you how you can make sure it is enabled   dont mind anything else said in this video and only focus on making sure it is enabled.

Then watch this video as this will share how to make it default within chrome.. You can clear your cookies and cache totally and the re visit the easywebinar Go live page so that it will ask you again for access this should now ask to allow access for the actual cam you want to use.