iMac Facetime built in camera

I have a brand new iMac desktop computer. The built in camera’s green light goes on (so it works) but the image is not projecting. I get a black screen. This problem occurs with Skype, PhotoBooth, Facetime & Zoom. I have done most troubleshooting to no avail. The computer OS is Catalina. Does it need to go to a medic? Thanks.