Uno r3 - Can't get USB Keyboards to work with an USB Host Shield
see last paragraph of this page https://github.com/felis/USB_Host_Shield_2.0

it says this:


  FAQ
  
  When I plug my device into the USB connector nothing happens?
  
  Try to connect a external power supply to the Arduino - this solves
  the problem in most cases.
  
  You can also use a powered hub between the device and the USB Host
  Shield. 
  
  You should then include the USB hub library: #include &lt;usbhub.h&gt;
  
  and create the instance like so: USBHub Hub1(&amp;Usb);.


your keyboard may be multiple HID devices with a USB hub to connect them