please provide some info on the monitor and video card so that someone can help you out. Without that information, it's hard to give suggestions.
Are you sure it's starting X?
Usually if X fails to load it's a video card/monitor setting problem.
MDK is usually pretty good about auto-detecting video cards and monitors, though. Can you boot up Windows and check the Windows configuration for your video card and monitor?
If you can find that out, use it in your X configuration.