First make sure you have your primary Taskbar set to show all windows. The easiest way to do this is to right-click on an empty area of the Taskbar and select properties. Deselect the “Show Taskbar on all displays” option then click OK. This will show all open programs on your primary Taskbar making it easier for us to move those ‘hidden’ windows.
This is most likely to apply to people who sometimes run their laptop with a second monitor attached. It’s a little different for me.
I usually run two monitors on my desktop. My second monitor is down because I gave its’ power cord to my friend who needed it for their computer. I have another power cord on the way but in the mean time it created a problem of apps I usually open on the secondary monitor opening to a monitor that isn’t there; Thus I’m unable to see the window to move it with the mouse. Oops.
Give the hidden program focus by clicking it’s Taskbar icon. Now press the Windows Key on your keyboard along with the left or right arrow key until the Window shows up on your screen.
This is really simple but something that took me a bit to figure out. I’ve gotten so used to pointing and clicking with a mouse over the years that I forgotten lots of keyboard shortcuts.