- Use ALTTAB to switch to the off-screen application.
- Press ALTSPACE to bring up the system menu (you won't see it because it is off screen)
- Press R to select the "Restore" menu choice to ensure the windows isn't is maximized (you can not move it if it is maximized)
- Press ALTSPACE again, then M to select the "Move" menu choice.
- Press one of the arrow keys to initiate the movement.
- Now just use the mouse to place the window where you want.
If you are using a non-english version of Windows, the "R" and "M" menu choices probably wil be different.