let me get you the story:
------------------------------------------------------------------
To reinstall Windows Defender, visit the following Microsoft Web site:
http://www.microsoft.com/athome/security/spyware/software (
http://www.microsoft.com/athome/security/spyware/software)
3. If this issue is not resolved after you complete step 2, follow this step:a. Click Start, click Run, type regsvr32 + one space + file name, and then click OK.
Note In this step, file name is a placeholder for the following files.
Repeat this procedure for the following files:
• wuapi.dll
• wuaueng.dll
• wucltui.dll
• wups.dll
• wuweb.dll
• atl.dll
• softpub.dll
• wintrust.dll
• initpki.dll
• mssip32.dll
-------------------------------------
from:
COMPAQ, Windows XP Home Edition, HP Total Care:
Help and Support Center: windows defender
You are most welcome.