Are you sure the motherboard is in the case correctly? Perhaps when you put the card in it is shorting on the case?
Yes was meticulous about installing MoBo, as I said it works perfectly with the XFX Radeon 6970 HD in there, that has the same interface double slot PCIE. Also works perfectly with no card in there.
Try it with the 1kW PSU "straight up" just to rule out a power issue.
I tried this shortly after trying the PSU plugs from the 1000w for the same reasons.