Warning
Create a Time Machine backup before major updates, disk operations, or security changes on macOS.
What you will achieve
Systematic boot failure diagnosis — know when it is software, disk, or hardware.
1) Rule out power and display issues
- Test charger, cable, and outlet.
- Disconnect docks and external displays for first boot attempt.
2) Try Safe Mode and Recovery
- Apple Silicon: hold power for startup options.
- Intel: hold Shift for Safe Mode, Command + R for Recovery.
3) Run First Aid and reinstall macOS
In Recovery, run Disk Utility First Aid then reinstall macOS if needed.