welcome to the forum.
I suggest you try to repair the avast installation start>control panel>add/remove program scroll down to avast and hit uninstall when the uninstall window comes up for avast hit repair did that help? if not try and installation from scratch uninstall avast reboot clean any left over registry keys with program like ccleaner. download and install the latest packet of avast at avast.com or filehippo.com reboot your pc.
good luck.