If you're using a wireless keyboard, plug it into your Mac, if possible.Some keyboards have a light that flashes briefly at startup, indicating that the keyboard is recognized and ready for use.
#HOLDING ALT KEY ON MAC BOOT MAC#
You might need to wait a few seconds before pressing the keys, to give your Mac more time to recognize the keyboard as it starts up. Then press and hold the keys as your Mac starts up. Then press the power button to turn on your Mac.
If a key combination doesn't work at startup, one of these solutions might help:
Or use Option-D to start up to this utility over the internet. Disabled when using a firmware password. D: Start up to the Apple Diagnostics utility.If your Mac is using a firmware password, it ignores this key combination or starts up from macOS Recovery.