Sometime your system may loose it's link to some DLL files. This may stop Windows from Updating.
With Dial A Fix you can run the program, Tick all and this will (Well should) fix your problem
Download here
http://www.softpedia.com/get/System/Sys ... -fix.shtml
Or from TM member barmanmyk
http://windowssecrets.com/2007/09/27/03 ... -XP-repair