Hi Diane,
It sounds like you're having some trouble with the camera on your Mac and I want to help.
Let's start by trying to start your Mac into safe mode:
Use safe mode to isolate issues with your Mac - Apple Support
If the issue persists into safe mode, let's see if your Mac detects the camera in the System Report.
Go to the Apple menu () > About This Mac > System Report > Hardware > Camera.
Is your camera detected here?
If your Mac isn't detecting a camera, you should contact Apple Support or visit the nearest service center, such as an Apple Store or Apple Authorized Service Provider, to seek service options:
Contact - Official Apple Support
Apple - Find Locations - Location Selector
Good luck!
Thanks for using the Apple Support Communities.