Macbook Won't Turn On, Clicking noise, not an HDD problem

Hey there,
Hopefully you can help with my black macbook. A friend was using it on low battery and it turned off due to it having no battery power (silly). When I tried to start it up while plugged in, nothing happened. I proceeded to let the battery fully charge (can tell by battery lights), and still nothing. The power adapter works and lights up. When I press the power button, nothing happens on the screen or anything. The only thing that I visually see is the power adapter changes color for a second after pressing the power button. I did notice that there is a clicking noise as long as I'm pressing the power button. I blamed the hard drive at first. When I took the hard drive out though, I noticed the noise was still there when I'd press the power button. What can be the problem if it's not the HD? Fan? Motherboard? Which one of these would make the computer do nothing but click and have the power adapter light change when I press power? Thanks