I had no problem running two, three or four servers on the same machine, as long as they had correctly set-up ports.
Have you tried disabling the firewall to see if that helps, have you looked at the game server logs to see if there was some messages showing that there was at least some attempts at connecting? (using Direct Connect. Don’t trust the steam list of the server browser: It’s not because the server does not appear on the list that it is not up and running)