In Windows Vista you can choose the way Power Button is akting. You can set the following options: Do Nothing, Sleep, Hibernate, Shut Down. It is set to Shut Down by default.

To change Power Button action you need to do the following:

1. Click on Start and then Control Panel.

2. Click on the Hardware and Sound link.

Note: If you're viewing the Classic View of Control Panel, you won't see this link. Simply double-click on the Power Options icon and proceed to Step 4.

3. Click on the Power Options link.

4. In the Select a power plan area, click on the Change plan settings link under the preferred plan for your PC.

5. Click on the Change advanced power settings link.

6. In the Advanced settings window, click on the + next to Power buttons and lid to show the available options.

7. Under the Power buttons and lid option, click on the + next to Start menu power button.

8. Click on Setting: under the Start menu power button option to reveal a drop-down box.

9. Choose either Sleep, Hibernate, or Shut down.

10. Click OK and then close the Edit Plan Settings window.