My MacBook Air won't connect to wifi I bought a new MacBook Air and was able to connect to the internet at first but now it won't connect.  I have other devices as well as other computers on wifi but my Mac won't connect.  When I try and click on the wifi, it tells me that it can't be joined.

How can I troubleshoot?
Option click the wifi icon in the menu bar and select Wireless Diagnostics.

Follow the instructions and post a second question if you get stuck with a specific step or can't narrow down the issue.

Also, carefully read the help guide on how to be specific and show how your research such as what version of OS X and what router is not working as expected.