When you press the power button of your Windows Vista PC, you will see that it doesn’t shut down by default. Windows Vista makes the system enter into sleep mode. This mode allows you to restart your PC and log back to Windows Vista very quickly.
However, there are people who prefer to shut down their systems when pressing the power button. In this tutorial we will show you how to change what the power button does.
First, go to Control Panel.

Windows Vista Control Panel
You can find the Power Options in a number of ways. The fastest way is to type the word ”power” in the upper right search box. Windows Vista will return the shortcut for the Power Options and a number of options beneath it.
Click on the second option - Change what the power buttons do.
Windows Vista Power Options

As you can see, the default behavior of the power button is entering sleep mode.
Windows Vista Power Options
Click on the drop-down list, select Shut down and click on the Save changes button.
Windows Vista Power Options
There you have it! The next time you will press the power button, Windows Vista will shut down your PC as Windows XP did.


Source Site: Windows Vista for Beginners - Windows Vista tutorials
Source Article: Changing what the power button does