Need Help

It sounds like ether the video card is bad or the motherboard will not support it. Did you check to see if the first board would only take a few kinds of video cards?
Did you go into the bios to see if video on board was enabled? Buy a cheap video card, you can get one for $20 or so to see it works. The video card you have may have been damaged on the first board.
If you do have on board video have you tried that? What O/S are you using and what kind of video card did you sell?
Did it go through the boot process, power supply fan comes on, you may hear a beep, lights on the computer for floppy, cdrom and keyboard?
Did you try to reseat the memory, cables ect?

Well I tried a different video card, almost exactly the same as the old one I sold. First I tried it on the first motherboard before the new video card and part of the board fried, which I just noticed. But neither one of the cards made anything show up on the monitor with the 2nd motherboard. The card I sold was a GeForce FX 5700LE and the card I tried was a GeForce FX 5700 I believe. My new one is a Radeon X800 Pro, they're all AGP. I don't have onboard video and my processor is Pentium 4 2.4GHz. When I turn it on the power supply fan runs, cd and floppy drives operate, no beep even though I don't think it ever did when it worked. I did try to reseat the memory and cables but still nothing.