Reinstall El Capitan or Later Without Erasing Drive
Please be sure you back up, if possible.
- Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
- Choose Disk Utility from the Utility Menu and click on the Continue button.
- After Disk Utility loads select the target volume (usually, "Macintosh HD") from the side list.
- Click on the Erase button in the Disk Utility toolbar. A panel should drop down.
- In the drop down panel set the partition scheme to GUID. Set the Format type to Mac OS Extended (Journaled.)
- Click on the Apply/Erase button and click on the Done button when it is activated.
- Quit Disk Utility and return to the Utility Menu.
- Select Install OS X and click on the Continue button to re-install macOS.
This will install the same version of macOS that you had previously installed.
