When you connect the AC adapter to the laptop, what color is the light on the AC plug? Does it appear to charge the battery? Or is there no light at all? Knowing this info will help determine whether or not your laptop is basically intact, or experiencing more severe issues.
I would remove the battery during troubleshooting in order to avoid complicating the situation. Also, definitely test the RAM -- reseat both modules, and then try powering on with one module in place, and then if that doesn't help, move it to the other slot, and try again. Lots of these machines suffer from a bad RAM slot and won't turn on when memory is in that slot.
Otherwise, try resetting the PRAM like Mayer suggested...sometimes that can "wake up" a machine.
If none of this helps -- and especially if there is no light on the AC plug -- you'll want to remove the topcase and see if you see signs of liquid damage, i.e. corrosion. If so, clean it off with q-tips and 90% rubbing alcohol, let the machine dry, and see if that makes a difference.