When you work with multiple monitors, sometimes a window will spawn or move inaccessibly offscreen, like onto a monitor that is plugged in but off/broken/in-use-by-something-else. If you’re in gnome there’s an easy way to grab the sucker and bring it into view.
alt-spacebar, then press m
This will attach the window to the mouse cursor so you can move it. Just move the mouse until the window is in view. Voila.