I had this problem myself, and I've finally found a solution that worked for me.
Open a command prompt (cmd), you might have to run as administrator, and type in "netsh winsock reset" and press enter.
That's it, you should be able to start new games and join online games now.
Hope this helps other people, because I was searching on and off for 2 days trying to find a solution.
Last edited by Endevin; 03/11/15 07:45 AM.