yes, it is a modular PSU
This means that rather than one mess of cables snaking out of a PSU, that there are specific individual cables/connections for each area of a mainboard ie. "module"
The pci-e cabe usually comes with your 1337 powered graphics card. If I were you, I'd
contact the place you got it from to inquire about the seemingly missing cable!
Funny that you havent tried booting it though