irq

I have an Asus P8B75-V motherboard. My GPU is using the PCIe x16 3.0 slot. I installed a 3ware 9650se in the PCIx x16 2.0 slot and it didn't work. Contacted Asus and they told me that only a graphics card would work in that 2.0 slot. Apparently I can only use the two slots for the same purpose...