Anyways on that page you can clearly see a 24pin power connector for the motherboard near the bottom middle (its white). Don't forget to also plug in the 8(4+4)pin CPU power connector as well on top top right (white).
Which board? This is the ASRock Ext3 Ge3 I made a red circle where the case led & power/reset buttons plug onto. Its on the very bottom right corner of the MOBO.