My PC won't boot at all after fitting graphics card?

Could be your power supply doesn't provide enough power for all the hardware. Also, you might wanna try taking out your batter on the motherboard to reset the bios. I installed a card a year or so ago that wouldn't boot until i reset the bios. Also, if you're board is pci e 1.0 and the card is a 2.0, it may have problems.