A least I made a lot of money in a few minutes just because a graphical administration tool for firewall was not functionning correctly. So, do you want to be sure, you don't have any firewall rules in action ?
In the affirmative, open a console windows and type iptables -nL
you probably have in your /etc/init.d something called firewall, service firewall stop, iptables -nL again
Try your connection now ...
I suggest you to verify your network settings with ping, traceroute, tracepath, route -n, may be you have something wrong.
Have a look into your /etc/resolv.conf