Microphone works unless the call is initiated by me

I am able to participate in zoom calls initiated by someone else and for which a link is sent to me; everything works fine in that situation.  But if I try to initate a meeting myself, my microphone can't be found.  The video works fine, the audio is fine, but I get a message that my mike isn't working and that I need to use a different one. 

I've checked my (PC windows 10) permissions, and the zoom desktop app is approved to access the microphone. I've looked at the zoom app itself, but I don't see any settings that would disable the microphone.  I can mute it, of course, but this isn't muting: it's completely disabling.

The webcam/mike I'm using is an old one, but it can't just be that because, again, it works just fine if I'm not the one starting the meeting. For what it's worth, I using the most updated drivers and the mike works fine in other applications.