Problem with ATi 4870x2

hi guys,

I am having problems with my PC since the moment I've bought it. It has never done what I've expected it to do, it is slow and useless (in gaming). I don't know why, but ALL games I play lag (even on low spec.).. I've just found in GPU-Z that the card is running in PCI-E x8 (the second chip is even in x1 mode) all the time, even if I play games or try any render test. My motherboard does support PCI-E 2.0 x16, so why it is running like a piece of ..? sorry but I'm really upset of this. Or can it be a problem with any other component ? I have latest CCC and drivers for all of them. Also, no overclocking has ever been done. here are my PC specs :

CPU : Intel C2Q Q9400 @ 2.66GHz
GPU : ATi 4870x2
MB : ASUS P5K PRO
PSU : Fortron 1000W
RAM : Kingston 4GB (2x2GB) DDR2 @ 800MHz
HDD : Seagate 1TB SATA
OS : Win7 x64

pics from GPU-Z :
card (chip) 1


card (chip) 2


thank you for any effort.