AF400FTZ Power Shutdown

Maybe someone has some ideas. My AF400FTZ shuts down after a few minutes of inactivity, as stated in the manual. What does not happen, though, is when I press the shutter release on my PZ-1P, the flash does not power back up. I have missed numerous flash shots because of this. Any ideas why this does not work? Would the newer 360 flash do anything different?

There is something wrong with either the flashgun or the camera. The 400 definitely should switch itself back on.

G