That card is PCI-E 2.1 and 2.1 cards sometimes have issues with older 1.x slots. If your motherboard is lower than 2.0 that could be the problem. If so there's a chance there is a BIOS update for the motherboard that deals with the issue. If not then there isn't much you can do.
Another question is whether or not your power supply can handle the card.
I thought PCIe cards of later versions were totally backwards compatible with slots/boards of earlier versions. No?