Updating bios didn't help

so here are two scenarios, one doesn't boot, one does boot.
1) I messed around with the power to the GPU. With both plugged in, nothing happens not even the onboard works, I can tell that the pc doesn't even start up.
2) With one power plug out (or both, or GPU out completely) of the GPU, the onboard ONLY works. PC starts up and everything else works fine.
Seems like my TPC 812 cooler only uses 2.4w. Is it possible but very unlikely that this is tipping the XFX 550 beyond its capability causing the problems. Its getting late and I don't want to install my old cooler right now to test. But what you guys think?
just for interest sake here is my rig if anyone is curious
i5-4670k (not OC'd)
Western digital 2tb
G.SKill 2x8GB
Asrock z87 Pro 3
XFX ProSeries 550
Coolermaster TPC 812
If I can't get this sorted by the w/end I'll probably take my machine to a pc shop...
Just irritates me, the more I think about it the more I think that I couldn't have ruined the card... But maybe somewhere along the line I did.
Refering to scenarios 1 and 2 it just makes me think that this may actually be a power issue because the PC doesn't even boot up when the GPU is connected - nevermind the display not showing anything.
Sorry, probably typed the same stuff all over in this post but my head is going crazy with this problem.