Please give some more details, such as make and model of the card, what driver you're using, and the relevant parts of your xorg.conf file such as serverlayout, serverflags, screen(s), device(s), display(s) & monitor(s).
Also, how many plugs on this card? 2 or 4 (I know you said QUAD but what does that mean), i.e, why does it use a (normal?) splitter?
Have both displays *ever* worked, or is this a fresh install or has never worked yet. I get the impression that it 'suddenly' went white, but it worked before just fine. In that case, I'm not optimistic it's software related; sounds like hardware.
EDIT: And please, what operating system is it?