Solution for your problem that i tried and tested by me.
2nd Part of the solution.
Go to avast!UI->click settings->click active protection->click web shield button slider-click disable for 10 minutes->now click firewall button slider->disable for ten minutes->wait for a while usually around 2 to 5 minutes(depends on the circumstances)->re-enable all shields(web shield and firewall shield)->click ok button->exit avast!UI on the upper right of the screen->check if your internet connection is working.
If not reboot your modem,router,disconnect your ethernet cable etc.
Connect it again and follow the second part solution.
Disable your windows firewall since avast! Internet Security or avast! Premier is enough and much more stronger and better than windows firewall.
The 2nd Part solution is temporary the problem may come again follow the steps that i gave to you.
If problem persist contact avast support through the original one and not avast! Tech support(using avast! tech support is a third party support that avast hired which is not recommended if you want your problem to be fixed.) contact them using email.
(
http://www.avast.com/en-us/support)
I wish this solution will help your problem to be fixed.
Best Regards
David1008