How to Fix Missing Network, Clock, Volume, and Power System Icons on Vista

For some reason, after a reboot of Vista, some of my system icons were missing. I wasn't able to simply re-enable them in the notification area, but a registry edit found here fixed it:

The problematic issue can happen if Windows group policy disables the Clock, Network, Power (or Battery), and Volume icons, or the registry keys related to notification area icons have corrupted. To re-enable and restore the check boxes, and hence user able to restore these system icons on notification area, the policies have to be turned off, and the registry keys reset, cleared or fixed.

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