Mac camera is not available for any application
Current social restrictions require use of integral camera, rarely used previously (so don't know how long this has been an issue).
The camera is not available on either FaceTime or PhotoBooth. In the latter, Camera tab confirms "No camera available".
Re-starting Mac has not resolved the issue.
I have tried the sudo killall methods but get message saying "No matching processes were found".
I would be grateful for any further advice, other than return Mac for repair as I need it for many other uses at the moment and so can't be without it.
Are external Apple iSight cameras still available? If so, would this be a compatible resolution?
Any help gratefully received; thanks in advance.
iMac 21.5", macOS 10.13