Windows 10 Phantom Displays

Windows will occasionally show the system as having multiple monitors even if a second display is not connected, in this case when the user opens a program it could be trying to display it on another screen. 

Recovering an Off-Screen Window

The easiest way to recover a window that is displaying on a screen that is not connected is to hold down the Windows Key and use the Left and Right Arrows to move it into view. This keyboard shortcut snaps the window into positions so if using the the Right Arrow does not work after a few times then try the Left Arrow. 

Change Display Settings to Remove the Hidden Screen

Right Click on the Desktop and select 'Display Settings'. If this window does appear on the screen you can view try the trick above to bring it into view. Once in view click 'Detect' in some instances this will make windows realize there is no other monitor connected. 

If the above didn't remove the extraneous display then use the dropdown in the Multiple Displays selection and select 'Duplicate these Displays'. Alternatively you can select 'Identify' at the top of the page and note which window is you can see, then in Multiple Displays select show only on X.