Step 3 Once the booting has finished, your Mac will display the Startup Manager to show you the available boot drives. To do so, you need to tell Boot Camp Assistant that your Mac supports the. Windows, Linux, or Mac OS USB Flash Drive (> 512MB capacity) Older Versions. If your computer still does not display the Boot Loader, it might currently be impossible to. EFI boot partition missing will cause your computer to have no boot. Step 2 Press down on the ‘Option’ key after restarting your Mac. However, some Mac computers dont support booting from external USB devices. Try using the same USB stick to start on a different computer. Step 1 Connect your external drive to your unbootable Mac. To do this, head to the Startup Disk preference setting in Settings.Įvery time the Mac starts, you can also toggle between OS X and Windows by holding down the Option (Alt) key immediately upon startup. How to Set the Computer Boot from the Bootable Media. Once you have Windows installed, you can set the default OS that will start each time you boot your Mac. Set the Default Startup OS or Toggle Between OS X and Windows The Mac will need to restart to complete the process and will automatically boot into Windows 10 when it's done. Follow the prompts to finish installing Windows.