So I finally gave up. Nothing my limited experience of computers allowed me to do - including what I thought was a clean instal - helped. Yesterday, there was a Windows update, which went normally. Today, it suddenly occured to me to try Netcam Studio again, as it originally went pear-shaped after an ‘update’, and Yay ! My cameras are back. Nothing at all done by me other than allowing the Windows update, so clearly, they have corrected something that they screwed up on the last update !