The ArcadeVGA should default to 640 X 480. If you select this resolution using the "Galaga" quickres icon on the taskbar, and the screen goes as in the picture, then you need to adjust the horizontal hold control. There should be a setting which locks at all resolutions, ditto the vertical hold. Some arcade monitors can't display 800 X 600 because that's 300 lines (interlaced) which is pushing the timing to the limits as these monitors were really designed to display about 240 lines, (ie 480 interlaced).