Computer not booting up at all after inserting video card?

go back inside ,make sure the card is fully snapped in place.i suspect if the card is properly plugged it is a system delima and your trying to run 2 video cards at the same time ,your motherboard video card and your new card at the same time,you probably need to deactivate your video card on the motherboard.you will need to go into your system CMOS (bios) page and deactivate the motherboard card and acknowledge the PCI card consult your owners Manuel for instructions.you might get information on this from emachines web site if you don't have the manuel.