I you are installing multiple video cards in a X58/P55 motherboard and you can't get into windows with multiple video cards in a system there may be an issue with the memory addressing for the memory on the cards.  in the BIOS under Frequency/Voltage Control or FSB/Voltage control go to Memory Features.  Set the memory low gap to 1, 2, or 3GB depending on how much total RAM is on your cards.  Then press F10 and enter to save and exit the BIOS.

If there is no change try each card alone in the system to verify there is no issue with one specific card.

If these suggestuions do not resolve the issue please contact our technical support team at 888-881-3842 or e-mail us at support@evga.com.