This can happen when your SketchUp window is larger than your monitor's screen. You can display the SketchUp status bar by clicking the "Maximize" button to maximize the SketchUp window (the "Maximize" button has an icon that looks like a computer screen and is just to the left of the "Close" button, the red button with the white "x").
You can also manually resize the window so that it is smaller by dragging down the top bar, and then moving the entire window up.
