Originally Posted by stren
Yeah I can still try the cards individually, but with the waterblocks on it's a real pain to change them in and out. That was why I got so many quick disconnects. But I'm using some of them on the water cooling test bench so I only have 2 pairs for CPU and GPU. The other thing I can try is plugging in the hdmi port of the gtx580, though I've never heard of a card defaulting to that and not coming up off the DVI. I can also try booting using the 9800gt with the gtx580 installed, then install windows and see if it can pick up the card once booted. I could then have windows default to run off the 580 and post can be to the 9800gt which could drive the same display via hdmi.
So I rebuilt the loop with a gtx 460 and a gtx 580, plugged the monitor into the gtx460, installed windows and the nvidia drivers. GTX460 could be seen just fine but no GTX580 showed up. So the only thing that had been niggling away at me was that the PSU cables could be used either way round. I'd used them the "wrong way" round on the 8 pin sockets because it was tidier. However tracing the wires back and forth makes it look like it's identical and the plugs used are identical. However getting rid of the "wrong way round" 8 pin cable and using a 6+2 made the 580 work!
So now I'm just plain confused. Now I have to break down the loop again, put all three 580's back in and see if it works with the right power supply cables