I had similar issue when I updated my Avast. I use Windows 7 so not sure if this will help you, but this is what I was told to do. I did this and can know open my Internet Explorer browser and go from there. Hope this helps you.
Please try to remove avast Online Security browser extension from your machine following these steps:
Please go to Start > Control Panel > Uninstall a program (Programs and Features, Add or Remove Programs)
Select avast! and click on Change. then uncheck the browser protection checkbox.