that's an almost obvious case of the web shield being denied internet access (explaining why https works)... no idea why it does that on your system, if it's indeed the web shield doing that. What do you want tus to tell you, 99% of people don't see that happen. There's nothing else I can suggest but uninstalling Avast + any other security software that you have, reboot, and do an install from scratch. And don't touch (don't know if you ever did...) the redirection ports for the web shield:
80,8080,8091,8081,8008,8888,3124,3127,3128
this is the default (found in general settings section, troubleshooting part). + keep ignore local communication checked. Check your proxy if you use one... probably not... reset your router to default etc... check your browser settings...
You got something on your system that blocks the web shield >>> it's not the web shield blocking http, it's something blocking the web shield in the first place, resulting in no internet access as your browser expects the web shield proxy to work.