Change the Windows Vista Power Buttons to Shut Down

The default action for the Power button on the start menu in Windows Vista is Sleep, which isn't necessarily useful for everybody. You can configure this setting easily by using the advanced power settings panel, which is a little tricky to get to normally, but we'll take the shortcut.

Open a command prompt (type cmd into the start menu search bar), and then type in the following:

powercfg.cpl,1

You could also take the long route (Control Panel \ Power Options \ Change Plan Settings \ Change Advanced Power Settings)

Once you get get to this dialog, browse down as shown to "Power buttons and lid"

From here, you can change the options:

• Power button action - Changes the hardware power button action
• Start menu power button - Changes the power button on the Start Menu

You can change the power button to either Sleep, Hibernate or Shut Down, or even nothing for the hardware power button.

source: http://www.howtogeek.com/