Are you sure you got all the drivers removed for the onboard video? I am also assuming you disabled the onboard video chip as well.
I assume the above is takne online as well. Offline there is nothing there.
Is the add-on a PCI, PCI-E, or AGP card?
What model of the NVidia? If it is a 6000, 6100, or 6200, then you might as well have stuck with the onboard video chip.