Originally Posted by LoneSierra
See the big contact on top of your camera? I'm pretty sure that's the "FIRE!" pin, so it's easy for that pin to make contact.
All those little pins are the ones that let your camera "talk" to your flash. If they aren't making good contact, you'll have the problems you're having. Try fresh batteries, wiggling the flash, and cleaning the contacts with a pencil eraser or any other contact cleaning method that YOU trust. I have the same problems with my 580EX IIs (we have four of them) on our Canon bodies (we have three of them).