Did you use TrenMicro removal tool to clear any leftover files?

General: Uninstalling a third-party antivirus software http://www.avast.com/faq.php?article=AVKB11#artTitle
Also here http://singularlabs.com/uninstallers/security-software/

When done, try avast repair
Controlpanel > ad/remove programs > avast > uninstall/change > repair option …wait a minute and reboot

Any change?