Computer won't detect my video card
I bought a GeForce 9800 GX2 XT a few weeks ago. It would not fit in my old case, and I needed a new power supply.
I bought a new TX750 watt power supply. nVidia said that was powerful enough to power two of my video cards if I decide to SLI, which I have planned in the future.
I moved the motherboard and all to the new case and installed the new video card (on XP). The computer came on and everything looks fine.
My monitor is connected to my onboard video card right now. If I connect it to the 9800, the monitor doesn't come on. I attempted to install the 9800 driver (nVidia 266.58), but it said the "Install cannot continue. This graphics driver could not find compatible hardware." And when I go to nVidia's website, I tried to auto-detect my drivers, and it doesn't find my 9800.
The video card is on (lights on, fans running).
My old graphics card was a nVidia 7100GS if it matters.
I don't think its a cable problem because my DVI works fine onboard, but not on the 9800 (the monitor won't come on).
My old video card works fine in the PCI-e slot. Wouldn't that mean the motherboard is OK?
My board is an Asus M4A78 PRO.
What should I try next?