Problems with graphics card.

I just built a new pc yesterday, and it only boots when the pci-e power cable from the psu to the gpu is not connected.
When I plug the power cable, the computer does boot up but shoes no display.

The fan does work in the mobo slot, but the pc just won't boot whenever I connect it to power.

I am currently using the on-board graphics.

I'm using gtx 560 ti.

Please respond asap!