Nvidia compatibility with old PCIE boards

Had this HTPC based on p4m890 via chipset that worked quite well. Wanted to enhance it's video performance so I tried adding it 3 different Nvidia cards I had (8600gt, 8500gt and 7200gs) and non of them worked under windows 7.
I replaced the board to another one I had (nvidia 570 ultra chipset) and the problem remained (Black screen after booting into windows 7).
I thought it's a fault of the OS, So I've installed windows xp, And after installing a driver from 4/2011 - It went black screen again after the reboot.
I'm afraid it has to do with some chipset compatibility, But not working with p4m890 AND 570 ?????

Are you using a psu that has more than enough wattage to run the cards?

I agree with Steve on this one. However I do have one note to add. I too have attempted this but with adding an older PCI card, the nvidia software would not recognize the old PCI card in their software and it seemed that Win7 had its own issues as well with the card while 2 PCIe were installed. If the PCIe were removed it saw the card fine.

Yes, The power supply is strong enough (It's a real 300W ps).
Anyway 7200gs consumption is very low anyway, And I know that all cards are working.
Still looking into it. Might be the images of windows 7 and xp I'm restoring. Trying to use older images, And if it wont work will reinstall fresh OS.