I don't know whether you already solved the problem, but here goes the hint:
Take a look at the system board's BIOS settings, Advanced tab, PCI configuration, PCI slot configuration, Option ROM scan. It's probably disabled for the slot you installed your card to.
Please keep in mind that this parameter only disables the controller's boot option, not the slot itself. So the controller can be used in the OS after loading the appropriate driver, even when this parameter is set to disabled.