Are you certain that you have the free version installed? I have just sorted out a similar problem on a PC by downloading it again and making sure that the free version was chosen instead of the free paid-for version trial offer. There is no firewall included so make sure that your Windows Firewall is turned on. Try this to see if it makes any difference.
There are many posts on the net about this and other problems relating to AVG 2013 but no real solutions other than to consider using a different free anti-virus such as Avast or Microsoft Security Essentials