Ok to cover all bases here is what I want you to do.
Uninstall AVG and stopzilla. You can reinstall them after we are done.
I need to make sure they are not blocking the browsers, I have seen it before.
Then we need to check the Windows firewall and make sure they havent been blocked in there by accented. So disable the windows firewall and after you uninstall the other two, reboot and then try the browsers.
Shane