The networking power management features on your computer allow it to save energy. The most common network power management feature used is called Wake on LAN. Wake on LAN allows your computer to "wake up" when you place your computer in "sleep" or "hibernation" mode. You usually receive a network message. You can wake up a LAN on Windows 7 by executing some steps on your computer.
1). Hit the "Start" button, "Control Panel," "Network and Internet" then hit "Network and Sharing Center."
2). Hit the "Change adapter" link at the upper left corner of the navigation pane.
3). Right-click your networkconnection you want to enable for power management and then hit "Properties."
4). Hit "Configure" and then add a check mark to "Allow the computer to turn off this device to save power" box on the "Power Management" tab.
5). Hit "OK" to confirm the settings.