Have you tried resizing the window?
How to resize an open window If that isn't the issue, try setting you vertical refresh rate (use 60 as a place to start).
How To Change the Screen Refresh Rate of Your Monitor If none of the above resolves the problem, most monitors have an On Screen Display (OSD) key - center the image there.
I suppose you could just maximize the window (assuming in windowed) - Press the ALT+Space keys and select Maximize Window.