When you add a new or used monitor to your computer, you may have to fix its automatic adjustment setting. The settings might have been perfect for what you had previously, but now you will likely need to tweak it so you can get the best possible picture. If you had an earlier model CRT type, and upgraded to an LCD monitor, these newer, slimmer, flat screens will work best if the monitors are set at the native resolution.
Click the "Start" button and then click "Control Panel."
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Click "Adjust screen resolution" under "Appearance and Personalization."
Click the "Resolution" drop-down list and then check the resolution that is "(recommended)." Note that the recommended resolution is usually the highest pixel display supported by your type of monitor.
Click "Apply," review the new screen resolution and then click "OK."
Click "Keep Changes" or click "Revert" to cancel the action.