PCs can save a lot of energy by being put in sleep mode. Most computers have power management settings that will send a signal to your monitor during periods of inactivity to go to sleep. These power management capabilities can be set manually to occur after a certain time period or a user can manually put the monitor to sleep whenever they're ready to with just a click of a button.
Click on your Start menu at the bottom of your desktop.
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Select the "Control Panel."
Double-click on the "Display" icon inside the Control Panel. On some systems, you may need to select "Performance and Maintenance."
Select the "Screen Saver" tab or the "Power Options" icon.
Click the "Power" button inside the "Monitor Power" box.
Select the time period that should pass before your monitor enters sleep mode. You can set your monitor to enter sleep mode after one minute of inactivity or five hours.
Select the "Advanced" tab and then select "Standby" under the text: "When I press the sleep button on my computer." This will allow you to manually put your entire system to sleep at the press of a button.
Turn off your computer and select "Hibernate" instead of "Turn Off" or "Restart." This option also will let you put your monitor to sleep manually.