WinXP SP3 Update messed up computer yesterday
 

(Posted for anyone else with the same problem.)
Yesterday, the yellow shield popped up saying Win Updates needed to be installed.

Rebooted, but things had changed.
The sound control and both networking icons had now disappeared on the task bar.
Hmm....?
The device manager window was blank (Settings/Control Panel/System/System properties/Device manager).
MS Security Essentials wouldn't update, saying there was a connection problem.

Was able to access internet.
The MS website said to enable plug-n-play (Start/Run/type in "Sevices.msc"/Plug and Play)

Did so, but got an error mssg pop-up: "Configuration Manager: The Plug and Play service or another requested service is not available"
Another window appeared, and I enabled Plug and Play.

Reboot.

Everything ok now. That seems to be the fix in case you have the same issue.
Strange because I've have Universal PnP disabled for years and never had this problem.

I updated the dozen computers here yesterday. None had any issues with the update.