Not seeing participants

When joining a meeting I can see main person running it and a small box with me in it.  I can see number of participants.  I can push to make box on right with names of participants but cannot see them.  I have been told to push top right box.  There is no box.  I  have done a test zoom and all of my video is working and I can see my self. When a participant is speaking I can see them.  Any suggestions?