Notification Area- System Icons are gone

I'm running Vista Home Premium (SP2), and I've noticed that the usual system
icons in the notification area are gone (not hidden due to inactivity)...the
standard Volume, Network, and Power icons. I've gone to taskbar properties,
and under the notification area tab only the "Clock" option is checked,
while the other 3 options (Volume, Network, and Power) are un-checked and
grayed-out, so I can't check them. How do I get these icons back? (The only
recent changes to my laptop have been the occasional "Windows Updates"...I
only approve "critical updates").

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Bob C.