Unable to set up Nvidia GTS450

(I think this post must be here, I saw the graphics section but it looked like kind of focused to software, anyway if it should be changed tell me)

Hi, first of all excuse me if there's any typo or grammar error,

I bought an ASUS Nvidia GTS 450 in order to retire my old 8400GS. So I bought a 550W power supply to avoid the power problem(also, I only use one hard drive and no audio card or anything that uses much power). After plugging the new videocard on the PCI 16x, I turn on the PC and the videocard won't send any video signal. But the integrated videocard does. I plugged the additional power supply's wire directly to the videocard and it's perfectly set up(I heard the "click"). I also tried touching BIOS but the system won't detect the card on(order of use) PCIE-->PCI-->IGFX neither PCI-->PCIE-->IGFX so it isn't BIOS bussiness(I think). To discard slot problems I just tried my old 8400GS and with the PCI-->PCIE-->IGFX it works BUT with PCIE-->PCI-->IGFX IT WON'T, that absolutely drove me crazy because I don't see any sense. I think I didn't forget anything.
PS:I tried reseting the system by taking out the battery(And it worked because clock got in 0)

Thank you every body,I have some aviate invitations, anybody who want one tell me.

I found a Tutorial by essenbe that might be helpful.

NVIDIA Drivers - Avoid Problems