[CCCleaner left color box on screen]

After a series of rebooting, the little square suddenly vanished.  I was going to send an image of it but the screen capture function wouldn't show it...  But it was there.  A colorful ghost.

[CCCleaner left color box on screen]

Downloaded and ran CCCleaner. Did a great job on the Registry, so I set it to clean the Internet browsers.  Seemed to be running smoothly when the screen went black.  Mouse pointer moved - but nothing on keyboard would affect anything.  A small - about half inch - color square appeared a few inches from the left side of the screen and a few from the bottom.  Then the system rebooted.  I signed on normally but the small square now is fixed in that location over anything on the screen.  What could cause it and how do I get ride of it.

Running Windows 10.  No other problems noted.