Open it up and disconnect the battery from the logic board. Removed the Mag-Safe adapter. Press and hold the power button for 5 seconds. Reconnect the battery. As soon as you reconnect the mag-safe you should get a spontaneous reboot. This failing, I need a detailed history of any problems you've had with the machine. Did you get a full install of ElCapitan? Has it been working? Been getting any spinning beach balls while trying to do things? Any liquid or impact damage? Do you have a paid for anti-virus protection program running. When you press the power button do you get anything, lights sounds?