Riavvia il computer.
Tieni premuto Command+Option+P+R all'avvio e verifica Macintosh HD
Esegui il reset della PRAM,
To reset your NVRAM, you use exactly the same procedure you once used to reset PRAM: Shut down your Mac, press the power button, and as soon as you hear the startup chime, hold down Command-Option-P-R. Keep holding down those keys until you hear a second startup chime. Then let go and allow your Mac to continue starting normally. Then check the Startup Disk, Display, and Date & Time panes of System Preferences to make sure they’re set the way you want them.
If you hold down Command-Option-P-R at startup and you see nothing but a gray screen that doesn’t change for several minutes—no Apple logo, no progress bar, no second startup chime—don’t panic. (This happened to me just last week.) The most likely cause is that your Mac isn’t registering the key presses due to wonkiness with a USB device. Disconnect all USB devices (except your keyboard, if it’s a wired keyboard), hold the power button down until the Mac shuts off completely, and then press it again and immediately hold down Command-Option-P-R. If that doesn’t work and you’re using an external Bluetooth keyboard, try plugging in a USB keyboard instead. If you’re able to reset the NVRAM successfully with the wired keyboard, you can disconnect it and go back to your normal Bluetooth keyboard.
Ripristina SMC, se tutto il resto fallisce
Before you can reset your SMC, you must shut down your Mac. After that, the procedure varies depending on the type of Mac you have.
Desktop Macs: Disconnect the power cord (either from the Mac or from the AC outlet). Wait 15 seconds and plug it back in. Then wait another 5 seconds and turn the Mac back on.
Portable Macs with non-removable batteries: Make sure the Mac is plugged in to AC power. On the built-in keyboard, press and hold the Shift, Option, and Control keys on the left side and press the power button. Release all the keys at once, and then turn the Mac on normally.
Portable Macs with removable batteries: Disconnect the AC power cord and remove the battery. Press the power button, hold it for 5 seconds, and then let go. Put the battery back in, reconnect the power cord, and turn the Mac on normally.
Questo potrebbe essere causato da un certo numero di cose, ma di solito è solo un problema tecnico in macOS.