Well, its not like hw is broken, but prly some combination of something is preventing win or driver to work properly.
Like that 6x290 on rev.4.. we never figured what is going on.. tried 32GB of RAM, all available BIOS-es, different BIOS settings, risers, etc..

Or that 'full logo show', just crazy - how exactly gigabyte logo at startup help BIOS to boot? ; )
I personally think, that GA BIOS simply does not work if GPUs report no display at all(and 290 cards do that) but 'full logo show' is bugged and ignores display info from GPUs and just outputs.. The truth is out there ; )

Ah, btw, if you have display plugged in, make sure that BIOS is visible at boot if not plug it into different card until you see it. Some mobos and later win go nuts if display is plugged into not 'init first' card.