If you can get no graphics at all, even at the initial POST stage, then it is likely to be one of the following:
Card not seated corrected in the AGP slot.
Poor monitor cable connection
New card is faulty.
My suggestion would be to reinstall the old card and boot into safe mode. If that works, try the new card again and ensure that it is seated correctly and cable is properly attached. If that fails (in safe mode) then it seems that there's something wrong with the new card.