When faced with a dead system we often need to be a bit more aggressive than just resetting the SMC as its often in a latched state.
Lets give this a try, carefully disconnect the battery and now with nothing plugged in press and hold the power button for a good 15 secs to fully discharge the logic board. Now plug in the MagSafe charger (leaving the battery disconnected) the system should spontaneously start up, did it? If it did let the system finish booting and do a proper shutdown. Now plug the battery back in and restart again, did it startup via battery?
Let us know what happens.