Go to System Preferences > Network, select the WiFi interface, click the action button (gear icon in the lower left), and select "Make Service Active."
This answer is based on the ifconfig reporting that en1 status is "inactive."
For troubleshooting purposes, try the following:
1) Remove the WiFi interface from the list of available network interfaces in System Preferences, restart the computer, then try to re-add it. If it's not listed as available...
2) Login as another user and see if the issue persists. If it does not persist in the other user, the issue is likely related to a preference in the user library of the first user. Instructions on how to find the user library can be found here.
The only item inside the user folder that MIGHT deal with network interfaces would be in "Preferences," but in my experience I haven't found anything in there that would deal with the network interfaces. If the issue DOES persist in another user...
3) Navigate to /Library/Preferences/SystemConfiguration/NetworkInterfaces.plist and copy it to your Desktop. Then move the original to the trash (you'll have to authenticate as an admin). Restart your computer and see if WiFi is detected.
NOTE: The /Library is sometimes called 'root' or 'local' library and is found at the root of your drive alongside "Applications", "System", and "Users."
4) If you have Mac OS X installed on an external drive, you can boot into Startup Manager and boot from that drive. If WiFi is still not detected in that external OS, it's likely a hardware issue. If it IS detected in the external OS but not detected in your internal (and the previous three steps did not resolve it), I'd reinstall Mac OS X.