Thanks, Walt. The only cloud service I use is dropbox, and only to transfer stuff. However, I did manage to copy and paste my pages to a new file and call it 'Test'. (but not after I'd lost a lot of work, unfortunately.)
That worked, but then I found I could not delete my original file. The message said the file was open in Designer, which was definitely not the case. I still got the error message, even after I closed Designer down. There was no instance of Designer open anywhere on my computer, but this got me thinking. I right clicked on my original file and opened it in Designer 1. It opened, I made a change and saved the change.
Then I tried to delete my orignal file ( so I can rename my 'test' file, but it wasn't having that! I received another error mesage saying the file was still open. I went back into Designer 2, to see if I could open it from there, but it wasn't in the recent files.
So, slightly mystified, I went back to windows explorer, to see that I had deleted it after all. (well, it was gone, anyway, and that was all I was worried about.).
So, perhaps something is going awry when files automatically transfer from Designer 1 to Designer 2 in the install.
I just nipped into Designer 2, opened a new document, dragged in a picture and saved it, so at least now I can save new files, which for some reason I couldn't do before.
This is in no way a fix, but it is certainly a work around for the time being.
I would like to thank you for answering my call for help.