Whether it’s an older MacBook or a cutting edge unibody MacBook Pro, Apple recommends the same troubleshooting steps for all Mac owners. For this article’s purposes we will be troubleshooting an Apple laptop that seems to be completely dead meaning that there is no video output on the screen and the power button seems to have no effect at all.
1. Is the battery plugged in and the MagSafe adaptor on? This question may seem redundant, but double checking that everything is plugged in correctly and in working order (including the power socket you’re plugged into) is the first step in the process. You can confirm that the MagSafe adaptor is providing power to your MacBook or MacBook Pro by checking for a green or red light. If the light isn’t on, try another outlet or unplug the MagSafe adaptor for one minute and plug it back in. The light should turn on.

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2. If your MacBook or MacBook Pro still won’t boot up, you should unplug any USB devices and other peripherals. If you’ve recently installed any user-replaceable parts like RAM or a hard drive you should double check that the new parts are compatible and fully functioning. You can do this by quickly swapping them out for the old parts. If the MacBook or MacBook Pro boot up with the old parts but not the new ones, then the new parts may be defective or incompatible.