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See this article for some troubleshooting steps that can help with the connection issues you're seeing:
Wi-Fi: How to troubleshoot Wi-Fi connectivity
It's not uncommon for you to "see" a great many networks, dozens even, yet you not be able to connect to any of them even if they are "open" (no lock icon). There may be a number of reasons for that, such as they're too weak for a reliable connection, or the router may limit connections to only specified devices.
There is only one way to achieve a reliable network connection, and that's for you to connect to your own wireless router. Even that doesn't work if its signal is too weak or if there are many competing wireless networks in your area.
If it's your own AirPort Base Station you're trying to use but can't, the latter could be the reason. The only way to mitigate the effects of wireless interference is to use 802.11n and 5 GHz whenever practicable. Even today you may only find one or two 5 GHz networks being used in an otherwise "crowded" area.