Sometimes, Windows Security Center stop recognizing your antivirus or firewall... The fix could be fairly easy for the most part.
1. Go to control panel and open Administrative tools.
2. Click on services.
3. Go down to Windows Managament Instrumentation.
4. Stop this service. Stop Security Center service too.
Let them to Automatically start.
5. Exit out of this area to your desktop.
6. Right click Start and choose Explore.
7. Go to c:\windows\system32\wbem\repository.
Delete this subdirectory
ONLY. Let the others there.
8. Exit back to your desktop and reboot your computer (maybe you need to boot twice).
This will rebuild the deleted folder and the database. Once restarted, Windows Security Center should show the correct info and antivirus and firewall should now be recoginized
Other answers for XP Security Center not detecting antivirus or firewall program could be found here:
http://support.microsoft.com/kb/883792.