Questions:
1) Are they same Make & Model?
2) Did you extend your desktop to the second card/monitor?
3) Did you you check your BIOS settings for the PCI-E slots?
4) Does CCC show any differences between the two cards?

I don't remember if the newer ATI's require a dummy plug for multi-GPU setups but if they do and you don't have the plug you could try plugging the second card into the secondary video port on you monitor. This is assuming of course your monitor has multiple inputs (Mine has four).