Can you be more specific?
When you power it on, you should get a red Pilot light when it's ready to fire. If you press the light (it's a button) it should test-fire the flash. That will confirm the flash actually works.
You can tell the camera to disable the flash... this is useful when you just want to use the flash's focus-assist beam to help the camera lock focus, but do not actually want the flash to fire. Check your camera menu... probably under "External Speedlite Control" -> "Flash Firing" and check that it is set to "Enable".
Tim Campbell
5D III, 5D IV, 60Da
