Some of the reasons your MacBook Pro fails to boot include:
• Its battery couldn’t store enough power to start
• Some issue with the power management system
• It couldn’t recognize the correct startup disk to boot from, etc.
Since your MacBook Pro doesn’t start, there’s nothing much you can do from within the operating system to diagnose and fix the problem. However, by pressing a few keys on your un-booted MacBook Pro’s build-in keyboard, you can bring it back to life, and can re-configure its settings once it boots up.
That said, if your MacBook Pro doesn’t boot, the two things that you can do are:
• Reset System Management Controller (SMC)
System Management Controller is a hardware chip in your MacBook Pro that controls the power-operated components such as CPU fan, LEDs, etc. Resetting SMC ensures that any corrupt information it has is erased, and the configurations are set to default.
• Reset Non-Volatile Random Access Memory (NVRAM) or Parameter Random Access Memory (PRAM)
NVRAM or PRAM (in older Mac computers) stores the information about system settings such as the startup disk to boot your Mac from, system date and time, screen resolution, etc. If any of these information gets corrupt, your MacBook Pro may fail to start properly or won’t start at all.
Here’s how you can reset SMC and NVRAM (PRAM) on your MacBook Pro:
Reset SMC
On a MacBook Pro without Removable Battery
1. Unplug your MacBook Pro from the power supply
2. Press and hold down the SHIFT + Ctrl + Option (Alt) + Power (Eject) keys together for 10 seconds
3. Release the keys
4. Press the Power (Eject) key to boot your MacBook Pro
On MacBook Pro with Removable Battery
1. Unplug your MacBook Pro from the power supply
2. Remove its battery
3. Press and hold down the Power button for 5 seconds
4. Release the Power button
5. Place the battery back in
6. Re-connect to the power supply
7. Press the Power button to boot your MacBook Pro
Reset NVRAM
1. Press the Power (Eject) button
2. Immediately press and hold down the Option (Alt) + Command + R + P keys together for 20 seconds (or until the screen goes all black and comes back to gray again, or you hear the startup sound (in some old models))
3. Release the keys simultaneously
4. Wait while your MacBook Pro boots
5. Get to System Preferences and re-configure the settings as needed
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