There is no text on the avast gui screen
Screenshot:
http://i.imgur.com/frvt04f.png
Perform a repair of avast.
If that doesn’t solve it perform a clean installation of the latest avast version.
Repair Avast:
Control Panel> Program and Features (Add/remove program)>Select Avast> Select Repair. Reboot when completed
https://www.avast.com/faq.php?article=AVKB204
If Repair doesn’t fix the problem, try the following:
Clean Install of Avast:
https://goo.gl/4Ptzkf