Are you running a crt type or lcd monitor? Adjusting the refresh rate could see an improvement if the monitor itself isn't showing signs of wear. Often on older crt monitors that close in on the some 17,000 to 19,000hr. life span you will start seeing indications that's time it for a new one. Lcds have a much longer 45,000-50,000hrs. according to reviews. While lcds have an auto adjust you can try the manual vertical and horizontal holds to see if that helps. How old is the monitor?