I'm pretty sure the 9600gt doesn't actually require a power cable, just the PCIe slot. Another thing that might be an issue is that your motherboard only has a PCIe 1 slot, whereas the 9600gt is a PCIe 2 card. You might not be getting a performance increase due to not being able to get enough traffic through the PCIe 1 slot. If your PC isn't booting at all, that's a whole other issue.