File Explorer multiple windows opening

I did that first, then closed down, restarted and the same thing happened.

Before the issue started, what exactly was changed or installed?

There were no changes or installations. I was trying to consolidate duplicate files from 3 laptops and was moving them in groups to see if there were duplicates. No problems for about an hour or so then the strange behavior began. Shut down, did a clean disk, shut down again then went back to work. Great for a little while, then it began again. I had two File Explorer windows open side by side and was cut and pasting files between them. Did all the above suggestions but it continually recurs. So...slow going now.