Download and install wga fix software then your win xp turns right again...
WGA Fix, Version 2.1 :, This fix installs a modified version of the KB905474 "WGA tray icon" update, as well as doing everything wga_v1.exe did. Version 2.1 adds compatibility for more users. If you've applied version 2 and it's working ...
www.technosquid.com/wga/
WGADiag2 will also fix the problem with registry key permissions may cause the installation of Windows Genuine Advantage Notifications KB905474 to fail from Windows Update: Here's a manual fix provided by Microsoft. ...
labnol.blogspot.com/2006/04/ workarounds-to-disable-non-genuine.html