What’s causing my MacBook Pro startup problems?

I have an intel core duo Macbook pro 2.16ghz. It won't start, when I press the power button I can hear the hard drive spin for 5 seconds or so then it stops, and nothing else happens. I know that it's not the hard drive cause I put another one in the computer, and it works as an external. I am afraid it's the logic board, does anybody know?
Yes, the battery is fully charged. Do you think apple would still deal with it if I've opened it? because the superdrive went bad, and I had to replace that. For you pc users, I went through two pcs in 3 years, had huge problems with them all the time, I've had this computer for 3 years, and it has been 10 times better