If the older computer BIOS doesn't support the options you're trying to add, then it may be fruitless. So, make sure you have the latest BIOS version and the latest chipset driver for the motherboard.
Hope this helps.
I have looked for months to find a new graphics card for an older PC that I built, changing it from an AIW pro PCI card to an AGP card. Until now, I could not get a signal either through the VGA or DVI ports. I finally found one that provides a signal through the VGA port but no signal at all on the DVI port.