Asus u3s6 compatibility p5n32-e sli

Hello,
I have recently bought the U3S6 USB 3.0 PCI-E x4 expansion card for my pc on the advice that all PCI-E cards should be compatible with all motherboards that can fit it, but I've found this not to be case at the moment. I have tried to get the card working on my 2 free PCI-E x16 slots, one of which caused the PC to not boot at all (although it would power on), which led me to believe the slot may be dead, the other slot i had a little more success with, managing to boot into windows only for about 5 seconds later, a blue screen flashes up and my PC restarts. In a desperate attempt to get a different result I have manually installed the drivers without the card being in the machine and @ have also activated PCI-E plug 'n' play mode in the BIOS. Could it just be the the motherboard is incompatible with the card? Other details of my machine are:
MB: Asus P5N32-e SLI
CPU: Intel Q6600
Graphics: Asus GeForce 8800GTX

Thanks in advance,
Liam