OS X El Capitan Will not Reinstall

Create a bootable installer for OS X Mavericks or Yosemite - Apple Support

Bootable USB Installers for OS X Mavericks to Sierra

First, review this introductory article: Create a bootable installer for OS X Mavericks or Yosemite - Apple Support. Second, see this How To outline for creating a bootable El Capitan installer. Simply replace the Terminal command with the one from the preceding article by copying it into the Terminal window.

You will need an 8GB or larger USB flash drive that has been partitioned and formatted for use with OS X.

Drive Partition and Format

1. Open Disk Utility in the Utilities folder.
2. After Disk Utility loads select the drive (out-dented entry with the mfgr.'s ID and size) from the side list.
3. Click on the Erase tab in the Disk Utility toolbar. Name the drive, "MyVolume". <---- IMPORTANT!
4. In the drop down panel set the partition scheme to GUID. Set the Format type to Mac OS Extended (Journaled.)
5. Click on the Apply button and wait for the Done button to activate. When it does click on it.
6. Quit Disk Utility.

Create Installer

Open the Terminal in the Utilities folder. Choose the appropriate command line (in red) depending upon what OS X installer you want. Paste that entire command line from below at the Terminal's prompt:

Command for macOS Sierra:

sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyV --applicationpath /Applications/Install\ macOS\ Sierra.app

Command for El Capitan:

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

Command for Yosemite:

sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ Yosemite.app

Command for Mavericks:

sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ Mavericks.app

Press RETURN. You will be asked for your admin password. It will not echo to the Terminal window. Then press RETURN again. Wait for the return of the Terminal prompt signifying the process has completed. It takes quite some time to finish. Be patient.

You can make a bootable USB stick to install using this free program which will do all the work for you.

Bootable USB Flash Drive – Diskmaker X

Because you cannot execute the command in bash. You need to boot the computer from a running system. Use the command to create a bootable USB installer. Boot the computer from the flash drive using OPTION boot.

1. You will need a running Mac that is booted into El Capitan.
2. Insert a formatted flash drive labeled, "MyVolume" into the computer.
3. Open Terminal.
4. Copy and paste the command line and press RETURN.
5. Enter the Admin password and press RETURN, again.

Boot using the OPTION key:

1. Restart the computer.
2. Immediately after the chime press and hold down the "OPTION" key.
3. Release the key when the boot manager appears.
4. Select the disk icon for the flash drive.
5. Click on the Arrow button below the icon.