Sounds like your new card is bad. What kind of power supply do you have? If your PSU isn't quite up to powering both cards that can cause issues, though usually not BSOD. If you are overclocking either of your cards, return them to stock clocks, an unstable overclock can cause bluescreen errors. If you are overclocking your CPU, try returning it to stock clocks. Once again your OC may not be entirely stable, or the second card may be pushing your PSU to its limits, and can't support two cards with a CPU overclock.
Only other thing I can think of is to hook up both cards and try reinstalling the drivers. Driver problems can cause a BSOD, but since you seem to be getting it only when using the new card, I doubt that would help. If none of these things work or apply to you, all you can do is RMA the card.