PowerPoint opens on second screen but I haven't one

This can happen when we have previously connected an external screen. If PowerPoint appears on the taskbar, right-click an empty space on the taskbar and select Cascade windows to see if it returns to the main screen.

If that doesn't work, hold down Shift and right-click the PowerPoint icon on the taskbar. Choose Move and when the 4-way arrow appears, press one of the arrow keys and move your mouse.

(Source: Bring Misplaced Off-Screen Windows Back to Your Desktop)

This did not work for me. Move never brought it to the screen. However, a Shift + right-click >> Maximize brought it to the screen. Then I clicked on the title bar and made is smaller and it stayed on the screen.