Recently tiny icons that look a bit like horizontal scroll bars have appeared on the screen. They cannot be moved, are always on top and nothing happens when they are clicked. Sometimes new icons appear or some disappear. Rebooting makes no difference. If what you want to click is under one of the icons it cannot be be clicked. It may be coincidence but the computer has also become very slow. It is running Windows 10
It is a bit difficult to describe so I opened notepad with a blank document and took a screen shot which is here.