Have you followed the instructions in the manual for troubleshooting? 

Which camera do you have? Are you using Liveview on your camera? Many 3rd party flash or triggers will not work with Canon Liveview. 

In the camera menu there is an option to disable  "Silent Shooting" while in Liveview. This should allow your trigger or flash to work while in Liveview.  

[![enter image description here][1]][1]

  [1]: http://i.stack.imgur.com/ErVuo.jpg