Customize the Shut Down Button

The default action of the Start Menu's Shut down button is to turn off your PC. If you want to use the button for another action, such as restarting your PC, you click the arrow to the right of the Shut down button and select an action from the drop-down menu.

What if you rarely shut your PC down completely but frequently restart it? You can change the Shut down button's default action to be Restart -- or Switch user, Log off, Lock, Sleep or Hibernate.

To change your default, 

Right-click the Start button and select Properties.
On the Start Menu tab, click the "Power button action" drop-down menu and select which action you want to be the default. 

Then click OK, and OK again.