welcome to the forum.

i suggest you try a clean installtion from scratch of avast and see if that could solve your problem.

download the latest version of avast from http://www.avast.com/en-se/free-antivirus-download

download the uninstall tool and run it.

http://www.avast.com/en-se/uninstall-utility

reboot your system.

do a registry clean with ccleaner to clean any lef over files of avast.

http://filehippo.com/download_ccleaner/

install the latest version of avast, registry the program.

good luck and let us know if you need more support.