White bar on right side of screen

Two days ago, a narrow white bar with a black area at the top appeared on the right side of the screen. It is the width of a sidebar and appears on the desktop screen with or without any programs being open. It sits right on top of sidebars so that I can't use the cursor to scroll. I had this problem with a different laptop two years ago and I believe it was an unwanted program or add-on that I had to remove, but I don't remember how I solved the problem. Of course, Dell tech support was of no help at all. Also, In the black rectangle at the top of the white rectangle, there is a white shape, like a semi-circle. I checked the screen function with the F12 key and this is not a hardware problem.