I gave reseating the memory a go, no luck. And yes, the 780 needs more power I see now. I just chucked it in there as a test, the 650 that is the card intended to be used at it calls for a 400W minimum which is why I got the 450. I tried unplugging my SSD and fans just to see, but same thing.
Is it possible that the card is somehow defaulting to the VGA output?