Patient problems with camera

Several of my patients are having problems with the video. Audio is working but they can’t get on the camera. This is both on laptop and desktop. They have tried several trouble shooting tips but nothing is working. What do you advise?

I have this issue with only one client who has Dell PC and uses Edge or Chrome. He reports that his video works fine with Zoom. And once in a while it works with Doxy.me. But occasionally, and lately every time, as soon as the “connecting circle” is completed it begins to dim and brighten over and over and client’s video never opens.