What I mean is that sometimes the "network" you see listed in the WiFi screen is not a legitimate WiFi network but a wireless router that is transmitting itself. A wireless router has to transmit itself so that your computer can find it so it can be configured.
For example, if you have an Airport Extreme and a laptop with an Airport wireless network card, your laptop will be able to find the Extreme so when you launch Airport Utility, you can configure the Extreme to have an unprotected network, or a protected network, or a closed network, etc. In the Airport Utility, you can name the Extreme, for example, "Bob" and your network "Smith". If you connect to "Smith" you can surf the Web. If you connect to "Bob" then you can't.
You may be trying to attach to the "Bob" as opposed to the "Smith".