You can see this message when the signal from the video card exceeds the maximum resolution and frequency that the monitor can handle properly.
When "Not Optimum Mode","Recommended Mode 1280 x
1024 60Hz" message comes up, disconnect the cable from the computer while the monitor is still
powered on.If there is a message coming up on the screen or if the screen goes white, this means the monitor is in working condition.In this case, check the computer for trouble.
Try to change the screen refresh rate ..to 60Hz .>
http://support.microsoft.com/kb/311403
Also visit the link below:
repair-samsung-lcd-monitor.html