Symptom
After choosing Log Out, Shut Down, or Restart from the Apple menu, a plain blue screen appears without the spinning disc cursor. The computer may not subsequently shut down or restart as expected. If you press the Power button on the keyboard (if it has one) a dialog box appears that says: "Are you sure you want to shut down?" If you click Shut Down, the computer returns to the Login Window or logs in automatically, depending on your preferences.
Solution
You can force the computer to restart by pressing Control-Command-Power, or by pressing the reset button on the computer. (It is marked with a triangle.) No data loss should occur when you do this under these circumstances because all open applications were quit and disk cache contents flushed to disk.
Then update to Mac OS X 10.1.2 or later to resolve the issue. This software is available via the Software Update feature of the System Preferences applications, or you can download a standalone installer from Apple Software Downloads (
http://www.apple.com/swupdates/).