tried avast repair and reboot?

controlpanel > ad/remove programs > avast > uninstall > repair option…wait a minute and reboot

any change?

also see this
http://www.avast.com/en-eu/faq.php?article=AVKB42#artTitle
http://www.avast.com/en-eu/faq.php?q=windows+security+senter#searchForm