Mac Startup

Press the power button then hold the following key or key combination:
Shift (⇧)	Starts in “Safe Mode”.
Option (⌥)	Boots to “Startup Manager” to choose startup disk (including network startup disk)
Option + D	Boots to Apple Service Toolkit 2 (AST2) for devices manufactured mid-2013 or later. Use in conjunction with diagnostics.apple.com on another computer.
N	Starts in a NetBoot environment (not compatible with iMac Pro or MacBook Pro 2018 and newer). Use this to boot to TechTools.
Command (⌘) + R	Boots to Recovery Mode. Used to reinstall the original OS that came with the device.
Command + Shift + R	Boots to Internet Recovery Mode. Used to install the latest OS supported by the device.
Option + Command + P + R	Reset NVRAM or PRAM (to troubleshoot booting issues)
Option + Control + Shift + Power	Unlike the other key combinations, press these while holding the power button and continue holding until the device chimes and restarts, then let go. Used to troubleshoot various hardware issues.

Tips

MagSafe light color: The color on the MagSafe charging adapter is orange/amber when the battery is not fully charged and green when it is.
Liquid Damage: Damage can sometimes be cleaned or removed and the device will appear functional, but may fail at any time. Our warranty on liquid cleaning covers repeat service, meaning we’ll clean it again, but we do not and cannot warranty or guarantee the fitness or longevity of the device.
“No Power” issues for MacBooks: These often turn into mail-in repairs for multiple component failure so prepare the customer to receive a $500+ quote for their device.
Data Recovery: In most “no power” situations, we can still recover data from devices with removable drives (generally 2015 and older MacBooks, most iMacs)