if you don't see any ping in the game server list, then it means the game is completely blocked to access Internet. In such a case, it's usually a Firewall and/or virus issue. If you see pings in the game server list but cannot host, then it's usually a router issue.
For the router, check if yours is here : https://portforward.com/router.htm
, then follow the instructions using the Port 4321.
With the demo, did anything work ?