Well, in that case, it cannot be avast! free that is causing your issues, as it does not have a built-in firewall and thus cannot have firewall drivers that would likely cause the symptoms you are seeing. I’d have a look at the NDIS drivers you may be running in your network system properties and report back what you find. These NDIS drivers are likely are native Windows drivers or third-party ones, but sadly, that information is lacking so far in your replies or in the description of your problems.

Please post back what you find.