Graphics Card Problems

I am running a Packard Bell iConnect with Win Me. It has an onboard graphics chipset. Recently I started having troubles running certain applications because no 3D graphics drivers could be found, although this was never an issue before. I have since added a PCI Nvidia TNT2 card, but it still does not work.
AGP cards are out of the question as the board does not have an AGP slot.
Some games still work fine and I have no problems setting different screen properties.
I have updated all the drivers, been through BIOSand the TNT card is showing in all device setings.
I am at a complete loss as to what to do….PLEASE HELP!!!
thanks
Chris