Another possibility suddenly springs to mind. There's a small possibility that your monitor and your graphics card aren't talking to each other properly and one of them thinks it's got a flat panel connected to it rather than a CRT (and vice-versa). If you check your monitor manual, you should find a selector button called "BNC/D-sub". Hit that and see what happens. There should be a diagram of the various monitor controls in the manual that points to its location.