How to Create a Recovery Drive to Rescue Your Failing Mac
Your Mac is failing to boot up properly due to some unknown glitch, so there’s no way to access the operating system or even get your data off the hard drive. A bootable USB drive, which contains a copy of the operating system, can save the day. This will allow you to check your drive for errors, restore a recent Time Machine backup, and—if the drive is still physically working—reinstall the operating system to give it a fresh start. First, you will need a USB flash drive or external hard drive formatted as Mac OS Extended, with at least 14GB of available space. You also need a download...
Source: pcmag.com