Two things: when you installed AVG are you absolutely sure there was no installed Kaspersky and if so you uninstalled it before AVG?
Can you try POTN for a brief moment with AVG disabled? Just for taking one item out of equation.
About proxy: when you load an web address the browser usually connects directly to that site, and downloads it to your PC. Sometimes your internet connection is behind a proxy, which means the browser does not connect to sites directly but requests the site content from an intermediate storage server which is locate nearer your home. That server (proxy server) browses the site you try to open, stores the data locally and then serves you the content of the site. The process is transparent, you do not notice the process in any way.
If data that proxy has stored is "flawed" you need to wait for the proxy to refresh that data until the site works normally. This is by no means a common situation, and proxies refresh data often, but it's one possible reason.