Please see, if you opened the Virtual Classroom in Chrome/Firefox browser. If not, copy the link of the Virtual Classroom from the browser bar on the top of the page, open the Chrome or Firefox browser and paste the link to the browser bar, then hit Enter. This will make you rejoin the classroom. If this was the source of the problem, in your new browser the audio and video sharing should work.
It's worth to check what you are sharing with the other participants by clicking the Media Share button. The "Audio and Video" option should be set in every case.
If you already use Chrome or Firefox browser, try to refresh the page. This rebuilds the connection and you will join the classroom again.
If the problem is still present, click the camera icon on the right side of the browser bar, if the connected devices are set up and the right camrea/microphone is selected. If you have more devices, please choose the one that is surely functioning.
If the problem is still present, copy the meeting link from the browser bar and close then open the browser again. Paste the link into the browser bar and rejoin the class by hitting Enter.