Clear the CMOS. The process should be in your motherboards manual. I think you can still do it by removing the battery on the mobo for a few minutes, but it would be best to refer to the manual on the proper way to do it. Usually it just involves moving a jumper to another pin then moving it back.
Is the new graphics card the same make as the old card, or is one AMD and the other Nvidia? If they ore different, you need to uninstall the old drivers, and then install the drivers for the new card.