|ATX mboards are always powered in some places, including some of the contacts in the ram and card slots, even when the computer is not running, as long as the ATX PS is connected to it and the PS is receiving live AC. |
Did you make sure you unplugged the power supply, or otherwise switched off the AC power to the computer, at ALL times, when you were fiddling with connections to the mboard and plugging in and unplugging cards inside the case ?
If you didn't do that at ALL times, you may have damaged the video card !
In that case, it won't work with ANY computer that has at least a 500 watt power supply.
BEFORE you try to boot the computer .........
Make sure that the video card is all the way down in it's slot, and that the bracket on one end of it is attached to the case. Some PCI-E X 16 slots also have a sliding piece that locks down the card at the inner end of the slot - use that if it has that.
If the card was / is not fastened down when the power supply has live AC power, merely plugging in the monitor's video cable can cause it to move upwards in it's slot and fry the card, and possibly the PCI-E X16 slot circuits too.
I'm assuming you have it plugged into the first PCI-E X 16 slot, the one closest to the center of the mboard. It may not work in the other slot unless there is a card in the first slot.