Zoom updated to the latest version and I can only see myself not the participants!

Hi teach lessons online so being able to see the student is very important. Since Wednesday the 24th of April, I can only see the students if I don't share a document - ie the lesson. Otherwise, in the window, I see myself for the hour.  I have uninstalled and reinstalled as not technical to see if that fixed anything. Would appreciate anyones advice- thanks in advance.