MacBook is displaying the message "no hardware installed" when I click on Wi-Fi I have a MacBook Pro 2009 running MacOS El Capitan. Recently the Wi-Fi has stopped working. 

When I click on the Wi-Fi icon it displays the message "No hardware installed", but Ethernet still works. 

Is there any way of fixing this by using a Wi-Fi dongle or something of the sort, if so do I need a specific dongle and how do I install it?
If you are getting the message "No hardware Installed" it means that macOS is not detecting your WiFi adapter for one of two reasons:


It's not installed (it physically doesn't exist)
It has failed


Chances are it's the second option.

You can confirm this by running Apple Hardware Test (AHT).  Hold the D key while booting from a powered off state with the AC adapter connected.  

Regardless if the first or the second, you will probably have to replace it with another Airport card



ifixit.com has an excellent tutorial and step-by-step guide on how to replace the board.  It's a time consuming repair - I wouldn't say difficult, but more detail oriented.  If this is not your cup of tea, I recommend taking it in for service.