Dell XPS 8900 POST failure

Recently I moved my XPS 8900's internals to a bigger case. When powering on, it appears to all work but when it gets to the dell screen, it goes black. I can press f2 or f12 for the setup menus but it never gets there. It appears to be a POST problem, with blinking power button and keyboard capslock and scroll lock LEDs. It blinks in a pattern of 3-7-1-6. I cannot seem to get it to boot. Anyone have a clue what the problem might be?

Thanks,

Colin