Solved Cursor moves off the page, left side only

Can't move the cursor off the active screen to the top, right or bottom. But when I move the cursor to the left side, it goes forever. I often do a split screen e.g. to look at two panels concurrently, you can go to the option between minimize & maximize (does this mode have a name???), move the panel to the right and you get a half-screen on the right. Do the same with another screen,...