@EvilSOB: I think I must have misunderstood you when you talked about joining two PSUs together. Just connecting the black and green cable sounds pretty safe and has nothing to do with what I accidentally did.
I did some research on this, and there was a Youtube video demonstrating this and I found a cable that does exactly that for ~10$. But I dont want to spend that money and I dont want to wait for that cable to arrive because Im doing this because I wait for a new/repaired PSU to arrive.
I don't want to cut the cables of any of the PSUs either...

When I get home I'll first try it with the harddisk. If that doesnt work I'll try to find a way to join the PSUs without cutting any cable.



@Quad: This might be true, but still I think it is obvious that the GTX 570 won't get enough power with only 400W, so the extra power must at least do something.

(Btw, Im pretty sure there is no GTX 570 Ti. Maybe you mean a GTX 560 Ti?)