Asrock Z77 Extreme4 second pci-express problem

[gab1213]

Hi, my second card is not recognised when it is in the second pci-express 16x slot, it doesn't appear in windows or in the bios. When there is only one card plugged in the second pcie 16x slot I can't see an image on the screen. I've cleared CMOS and updated the bios and there is still nothing.

The motherboard is the Asrock Z77 Extreme4 with an i5-2500k and both cards work.