Have you installed the correct monitor drivers? I've seen lots of sync problems between the video card and monitor when the video card tries to drive the monitor in an improper way, usually because the wrong monitor driver has been selected. Sometimes the monitor driver is just the "PnP Monitor", and that's not always the best. If you have the correct monitor drivers, try downward adjusting the refresh rate in Display Properties and seeing if your problem goes away. You may be over-driving the monitor, and that could eventually burn it out...