did you install necessary drivers for the card first? most but not all cards will automatically work. made sure all power cables are hooked up? GPU fan spins? troubleshoot the mobo as well by booting it as normal without the card,and if it does then you know its something to do with your new card.
i plan on buying the ASrock 970 Extreme3 next month, does the gpu size "length" block any SATA slots or anything like that?