macOS · Mac · Everyday fixes

Fix a Mac that won't start up

A black screen at boot is scary, but macOS has a recovery mode that fixes most of it without erasing anything.

Before you start

Medium risk. This change is reversible — you can return to the previous state without professional help or data loss.

If FileVault is on, Recovery asks for a user password before Disk Utility can even see the disk. There is no way past that prompt — no reset, no bypass. The password is the requirement.
In Disk Utility, switch on View → Show All Devices and run First Aid from the bottom up: physical device first, then the container, then the volume. Running it on the volume alone skips the layer that is usually the broken one.
'Reinstall macOS' from Recovery isn't necessarily the version you were running — on Intel Macs it can offer the one the machine shipped with. Expect a large download and several hours on a slow connection.
No chime, no fan, no light at all is a power problem rather than a software one. Try a different charger and cable before you go anywhere near Recovery.

Apple Silicon (M1–M4): press and hold the power button until 'Loading startup options' appears → Options → Continue
Intel Macs: restart and immediately hold Cmd + R until the Apple logo or a spinning globe shows
In Recovery, open Disk Utility → select your main drive → First Aid — this fixes most boot problems on its own
If that fails, choose 'Reinstall macOS' from the recovery menu — it reinstalls over your existing system and keeps your files

The Mac boots normally after First Aid (or a reinstall), and your files are intact.

First Aid reports unrepairable errors, or the Mac still won't boot — back up what you can before any erase/reinstall step.

Next stop: the related fixes below, or start a guided diagnosis.