ASUS GeForce GTX460 issue, help?

I just got my GeForce GTX460, installed it (although only 1 6pin plug was used because i don't have any others), but as soon as my PC boots I get a BIOS error (1 long, 2 short, GFX not detected in my case). Anyone have any tips how to help me out in this? Should I get some adapters for the second 6pin plug? Does the ASUS GTX460 need both plugs to work at all?



If anyone wants to know, my PC specs are at the moment:

500W Power supply unit

Intel i5-650@ 3.20 GHz

ATi Radeon HD5450 (changing to ASUS GTX460, both gfx cards with 1024 MB)

4GB RAM DDR3|||it needs to be compatible with the motherboard, so you can probably get a converter for a port that isn't compatible to make it compatible. It can ruin a mobo if you plug in the video card in the wrong place.