Gfx Card And Irq's

I am having alot of probs with my new system, basically I am unable to run games as well as I should for the specs. How can I tell if the system is actuallly seeing the vid card in the pci e slot. The card is def plugged in the slot. In 3dmark06 in the system details it says this about 1 of the pci e slots but I dont know how it says it is assigned to irq 0 when in dev mgr it says the vid card is in irq 18.

PCI Express Slot
Order 4
Designation PCIEX16_1
Type PCI Express
Characteristics 5.0V, PME Signal
Data Bus Width 0 b
Details In Use, Short
IRQ 0

It says I have 4 and the other 3 are available but on the mobo there is only 2 slots.

thanks in advance for any ideas.