The safety switch on the flash mechanism may think that the flash is closed if it is not fully extended.
Try holding the flash fully open in the upright position as you try to shoot a picture.
Let me know if the flash fires when you do that...
Did you try on both cameras?
I am unable to make a call at this time, however we can still reply back and forth here.
If my previous suggestion did not work, then there may be a software glitch or an incorrect setting on the cameras.
Try going to the Setup Menu and select Reset to reset the camera's settings...
Let me know if that works?
Ok if that did not work either then the cameras have a hardware fault which will require a repair at a service center.