my A4000D was doing something similar. Turned out there was corrosion around the crystal (I think that's what it's called the 4 Pin DIL connected box on the motherboard) which was causing it to not connect always and I would get a dark gray screen or a black screen with everything cycling but nothing else. So check those, I think they're called crystals, there should be 2 on the motherboard, they are socketed, so carefully pull them out and then put them back in the board in the exact same way you pulled them out, then try to boot the system. It's worth a shot.
Nathan
*edit* Flashing green indicates some sort of chip error doesn't it? When I remove my chip memory my screen flashes green. BTW is that floppy drive listed really rare? Someone here in town just gave me one of those drives today. I put it in my A600 cause the floppy drive is completely toast!
