System breakdown

I tried to install a new card into an HP system running XP Home. It has been showing the messgae “PAGE FAULT IN BLAH BLAH BLAH….What is a Page fault? and when I reinstalled the card,as the directions in the page fault error explained, I cannot getthe system to boot. I have to go to safe mode. Also I am being asked to activate windows again.Can any one tell me what the heck is going on here?