I've got vista home premium and had no problems with my anti virus software. Then a few days ago it stopped detecting my anti-virus. I'm using Avast Free Antivirus which is up to date and says it is protecting my computer, etc. I uninstalled it then re-installed it but to no success. The same thing was happening with AVG Free but I uninstalled and reinstalled, then finally deleted and am now trying Avast, but nothing has remedied the problem. Also windows defender is turned off, when I go to turn it on it says searching for definitions then says there are no new definitions to download and won't turn it on. My computer is all up to date with vista updates. Help on this would be greatly appreciated since I am not sure what is going on. I have searched through this thread and tried the advice given in this post (the part about restarting in safe mode) but it did not seem to work. http://social.technet.microsoft.com/Forums/en/itprovistasecurity/thread/911f514d-0017-4f72-b97f-ddde37b1a795