first thing you should do is put back your old card to see if the machine will post and have graphics.
if it does then you know the problem is with the new card.
Try reseating your cpu as you could have easily knocked agiainst it while installing that big motherfucker card.
when changing hardware in machines especially graphic cards..dimm memory can be a big problem,try reseating your memory,or changing dimm slots
your not running a asus rampage 2 exteme motherboard by any chance are you?
is the card damaged in anyway? any cracks or chips in the PCI slot?