If the current setting for the Start Menu power button do not meet your needs, you can easily change it (to sleep, hibernate, or shutdown) through the following instructions.
Editor Update: Several people have recently contacted me about switching the power button function either to sleep, lock or shutdown. I have republished this tutorial for their reference.
It should be noted that sometimes the OS will force change the action temporarily in certain circumstances. This frequently occurs when updates require installing. Once the forced action occurs, the button will default to the set behavior.
1. Right-click the Taskbar.
2. Select Properties.
3. Click the Start Menu tab.
4. Use the Power button action dropdown to select the desired setting (Switch User, Log off, Lock, Restart, Sleep, Hibernate, or Shut Down).
5. Click OK.
