9600gt only running at 450 mhz

Hello, I recently installed a Gigabyte 9600 gt OC. For those of you who aren't aware this is a passively cooled card that is supposed to run with a core speed of 720 mhz. Unfortunately for me however, in both cpu z and riva tuner, the speed is showing up as only 450mhz? Could this be because it is over heating and being underclocked? or perhaps it isn't getting enough power from the cpu (generic 450 watts), or could it besomething else completely which I am missing? Also I can run mw2 with everything at max so maybe its just being displayed incorrectly? cheers in advance