"I did the same thing: I initiated a restart, then held down the “shift, control, option” keys and hit the power button without plugging it into . My MacBook never started back up, same as the above post.
I followed the plan that the original post: opened the computer and pressed the small button adjacent to the internal lcd power light with the computer plugged in to the wall outlet. The charging alert rang and I knew my computer was back to life.
Do follow the disassembly instructions on ifixit when you are removing the screws and removing the bottom casing. The flex cables are very delicate."
For this model MacBook it is IMPERATIVE that the battery disconnect button be held for 10s (until the tiny led dies) before removing the track pad flex, else you can kill the logic board.
On power back up post repair it is IMPERATIVE that the MacBook be connected to a standard USB charger (5v 0.5-1a) until it powers on before connecting to the standard MacBook charger. This is to wake up the power management circuit. Connecting directly to a standard charger after having disconnected the battery can likewise permanently damage the logic board."