I used to have that problem with one of my amigas and I checked both 2xblizzPPCs....
I should add also that if my amiga was "cold" (first boot of that day) I needed to let her in that black screen for some minutes before I reset, otherwise it still couldn't boot.
the problem solved when I modified the power supply (atx) to sent from seperate cables power directly to amiga's floppy connector and giving more cables from atx to normal power input of my amiga...
although I can't be sure only for power because I can't remember if that was the period that I changed my amigas motherboard with another one...
PPCs are the same although.. and the problem stopped.
