Fail when Graphics Card is powered?

Hi
I'm building a system now, and it looks like I have, for the most part anyway, wired it correctly. Except for one part I guess.
Graphics card is inserted into the main PCI-E slot (one more to be added when I atleast get one of them working) and monitor hooked up to it. When started like this, it boots to "insert disk" or whatnot, and the GPU fan spins.
But the way I understood it, these cards need more power to function correctly, so when I hook the cable from my powersupply marked PCI-E to the graphics card and attempt another boot, the monitor gets no signal.
The PSU is hooked to everything else, and when not connected to the GPU everything else seems to work as well...

Help, is there something I'm missing here?

Antec Twelve Hundred Gaming Case
Two Gainward GeForce 9800GT 512MB PhysX CUDA PCI-Express 2.0, 2xDVI, HDCP, Graphics Plus, 3D Stereo
MSI K9N2 Diamond, nForce 780a SLI, DDR2, Socket-AM2+, X-Fi, ATX, 3xPCI-Ex(2.0)16
AMD Phenom 9850 Black Edition Quad-Core 2.5 GHz Boxed, 4MB Cache, Socket AM2+, 125w
Crucial DDR2 BallistiX PC6400 4096MB CL4 Kit w/two BallistiX 2048MB's, E.P.P
Corsair Powersupply 1000W, Black, ATX/EPS, 140mm fan, SLI

Does your mobo have onboard graphics? is it enabled? if so switch off in BIOS.