First of all check if you have the right browser. We recommend to use Google Chrome and Mozilla Firefox.
Check your Internet connection. Can you open other websites? Can you watch video on youtube?
Close all other tabs.
Check that you're not connected to the same conference through the other browser.
Try to shut everything down and connect again.
If it still doesn't work - text us in the chat, or reach us through e-mail: firstname.lastname@example.org