This might help you with your issue: http://www.insidemylaptop.com/turn-on-macbook-pro-laptop-without-power-button-locating-power-on-pads/#comment-2061303 Cheers.
Can anyone help me on this step, I damaged the head of the screw it is the screw near to the fan and the screw near to memory the rest of the screw I managed to get it off I'm so screwed :( any help is much appreciated. Thanks