Check the PCIe 6 pin and 8 pin rails. The regular 12 V rails are not in use for the GTX 480.
This one is the Rosewill RBR1000-M
12V1 is 24pin MB
12V2 is PCI-E 6 and 6+2 Pin fixed
12V3 is CPU 4+4, Peripheral, Floppy, SATA, PCI-e 6 pin and 6+2 pin (Modual 1)
12V4 is CPU 8 pin, Peripheral, Floppy, SATA, PCIe 6 pin and 6+2 pin (Modual 2)
1 & 2 are each 20 Amp rails and 3 & 4 are 30 Amp Rails. 4 rails total.
Picture of plate is attached. This should arrive Monday. I probably should have gotten the Corsair but I had already ordered this
In that case draw the 6 pin PCIe cable off V3 and the 8 pin off V4. Or at least draw them from different rails. Under load the GTX-480 can consume more than 420 W, or use more than 35 Amps.