Windows 7 Explorer Is Not Responding, Blue Circle Endlessly Rotating?

There is a perhaps related post four weeks ago, to which there have been no replies. I open Windows Explorer, and highlight a folder. Then hit the DELETE key. The little blue circle icon shows the light chasing its tail endlessly. Task Manager indicates "not responding" and when I hit the white X on red "close" button in upper right corner, I get an error window that says the same thing. There is only a single thumbnail.info file in the folder. If I try to click on another folder, the screen goes gray. This happens only recently, not previously.