Search "screen tearing". If what you are seeing is the same (brief flicker of the next frame across the top or bottom of the screen), then you will want to enable vsync in your games, it will match the frame rate of the game to your display's refresh rate, 60fps for 60 Hz for example. Note that this only really works well when your video card can exceed that 60 fps in the games you are playing, 7850 at 720p should be no prob.