Hello,
I own this very same computer, and I replaced the A/C adapter just a few months ago, when you plug the computer in, does the ring, around the power input, light up blue? Because if not, your computer is not getting a charge, so no matter what you do, it's not going to turn on. There are many guides here on iFixit on how to disassemble this computer down to the very shell it lies in, if you wan't to attempt replacing it too. I think this may be your problem, as this computer is notorious when it comes to the sensitivity of that A/C input.. I sure hope this helps.
-Samantha S.