I don't think this is an adapter issue. I believe that it has more to do with your wireless router. Disconnect the wireless connection and run a net cable direct to the MODEM. Cycle power to the modem, and retry. If you get connectivity, then it will be your router that is causing the issue. If there is still not connectivity, then contact your ISP.
(These are steps that they will want to lead you through anyhow...)
On another note, your router should have a way to administer the net. Before you try the first suggestion, with your current connection, try getting to the web interface by typing "http://192.168.0.1" in the address bar on your browser, and log in to the router. Check your settings.