MacBook Air wifi issues
I wrote an extensive post on MacBook Air wifi issues:

https://apple.stackexchange.com/a/70605/34078

It's not exactly your symptoms, but a good start. 

Take a look at the wifi equipment you are trying to attach to. If you can't still get a connection after reading my previous post, take the MBA back to the Apple store and see if you can connect there. If you connect, the issue probably sits with your wifi router. If you cannot connect, it's the laptop.