If your Intel-based Mac just flat out won’t turn on, you might want to try resetting the System Management Controller.
This chip is responsible for many low-level functions, including battery and thermal management, keyboard backlighting, and responding to the press of the power button.
To reset the SMS, follow these steps:
1. Shut down the computer.
2. Plug in the MagSafe power adapter to a power source, connecting it to the Mac if it’s not already connected.
3. On the built-in keyboard, press the (left side) Shift-Control-Option and the power button at the same time.
4. Release all the keys and the power button at the same time.
5. Press the power button to turn on the computer.
And of course, if you’re still having troubles after completing these steps, bring your computer into us for a full diagnosis and repair.