Canon 580EX Flash will not fire. Being shot on a Canon 5D Mark III.

Question

The light  does not start out green and stays red on the 580EX Flash. It doesn't even go into a sleep mode when not activated for a length of time.  Fresh batteries does not make a difference.  It will allow me to change settings but it won't fire. The infra-red displays it's test light but the flash will not discharge even when it demands it.  It is not on slave or wireless settings.  Nothing makes the flash go off, even the test flash.

Answer 1

First, the red light on the flash indicates it's ready to fire. It goes off when the flash is recycling.
That "pilot" light also is a test button... Turn the flash on and as soon as it lights up, press it. If the flash fires, then it's likely the flash is fine.
Next, check in your camera menu... is Flash Firing (which might be in a Flash Setup group on a later camera model) set to "enabled"? Silly little thing, I know... but it happens. Don't ask me how I know! 
Also check the flash is fully mounted in the hot shoe. The locking lever will not go all the way to the latched position, if the flash isn't fully seated in the shoe. The locking lever actuates a small pin on the flash's foot, that fits into a corresponding hole in the hot shoe, both to insure the flash is fully in place and to secure it there.
If all the above checks out okay, another possibility is the camera's exposure mode. Now, personally I don't use them so can't say for certain, but assuming your camera even has them, maybe some of the more automated "scene modes" such as the "running man" for sports, etc. prevent the flash from firing.
Again, I'm not certain how the flash will perform in those modes... But you should use Av, Tv, P or M to test the flash anyway. In the auto exposure modes Av, Tv and P, the flash will fire at reduced output, as FILL light. In the manual M mode, it will fire FULL, as the main light source. Often when firing as fill with reduced output the red light of the flash doesn't go out with a single shot... I often can get 2 or 3 pops out of it before the light goes out and the flash goes into recycle mode for a few seconds.
Is it possible the flash actually is firing, but as fill so it's not a very strong output and it doen't need to go into recycle mode? You might not see the flash, if it's at reduced power and you have your eye to the viewfinder (which blacks out momentarily during the short duration of the exposure). Usually you hear the flash "pop", but if shooting somewhere with a lot of background noise, might not even be able to hear that.  
Finally, are you trying to use the flash wirelessly? If so, then there are a number of possibilities. First, the flash needs to be set as "slave". Next, the camera's on-board flash needs to be popped up to act as the controller. Also, the flash and camera need to be set to a matching channel or group. Also, the flash may need to be rotated so that the red pane on the front is facing the camera. Plus wireless flash control is optical, so is "line-of-sight" only. And it's reach is rather limited.
Some of these suggestions may have already occured to you. If so, great! I don't know your level of experience with the flash or what camera you are using, so am just throwing out possibilities that occur to me. I hope this helps!
Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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