Disabling the Security Center is one of the favorite things viruses and spyware like to do, and it can be a sure sign of virus infection.
You say virus is unlikely with the utilities you have protecting it, but protecting it in the background isn't always enough. Have you updated the virus/spyware definitions for these applications and run full scans with them?
What I would do;
1] Disable System Restore. Viruses and other malware can hide in the backup files produced by System Restore points and anti-virus and anti-spyware utilities cannot remove malware from these protected files. Disabling System Restore deletes all the backup files. Be sure to re-enable it and create a new System Restore point once you are done.
2] Make sure all your anti-malware apps are up to date.
3] Reboot into Safe Mode and scan with each anti-malware utility, one at a time. In Safe Mode most malware cannot get started.
4] When you are done, boot back up into Normal Windows mode and visit the following for online scans;
a) Housecall at http://housecall.trendmicro.com and
b) Ewido at http://www.ewido.net/en/
Let them remove everything they find.
5] Re-enable System Restore and test the Security Center settings.
I hope that helps
We're on xp sp2. When I check Windows Security Center, it is often disabled. I've enabled it more than once via the procedure listed at http://support.microsoft.com/kb/919291/en-us but eventually (like after logoff/logon or reboot) it's disabled again. I even set Recovery to Restart on Failure and Logon as local system account. Virus is unlikely with Spyware Blaster, SpyBot, NAV 2007, and Ad-Aware SE protecting it. Any ideas?