computer crashing with new 3d card

what power supply are you running? How many times have you tried re-booting?

I remember having a similar issue to yours when I last upgraded my video card. It was still trying to read off of the onboard port for some off reason, even though the startup screen was displaying from the new card.

what was your old card? or was it onboard? if it was onboard, try shutting it off in your bios