I have this problem where one of my video cards won't light up. When I had the second card in the last PCI slot it would be fine but now in the second PCI slot it does this. When I first boot it will light up but when in Windows it will turn off, the light also comes on when I disable crossfire but when enabled it will be off. Only the first card always lights up. I also switched out the crossfire bridge but that made no difference.