Try repairing your WMi repository.
It happens frequently when database become corrupt security centre reports false status of AV and firewall.
try renaming the c:\windows\system32\wbem\repository folder and then restart your computer, it should solve the problem.
or alternatively follow the exact procedure from this link http://windowsxp.mvps.org/repairwmi.htm
also you can use methode described here http://kb.eset.com/esetkb/index?page=content&id=SOLN367