I have an open application on my Desktop that is halfway off the screen. How do I move it back?
Position the cursor in the top gray section of the application window then click and drag the window back onto your Desktop. Be careful not to click in the red/yellow/green buttons in the top left corner or on the closure lozenge in the top right.
If an Excel worksheet is partially off the screen or too large to access the scroll bars, select View -> Full Screen from the Excel menu and the window will reposition itself to fill your Desktop. You can then resize the screen as you like.
If an application or dialogue window is completely missing from your desktop and you have a projector connected to your computer, the computer may think the window is displaying through the projector even if the projector has been turned off. Select the Display or Display Menu icon in the Finder Menu Bar and select Mirroring Displays from the drop down menu. All open windows will be displayed on your Desktop.
If you don't wish to change the display setting, unplug the dongle connecting the projector to your computer, then replug the dongle and the missing windows should appear on your desktop.