Q: Installing el capitan

Hi,

Make sure your Mac meets El Capitan requirements here >  Upgrade to OS X El Capitan

I provided the solution in your last post of your question. You should avoid posting duplicates.

Reinstall El Capitan Without Erasing Drive

 

Please be sure you back up.

 

1. Restart the computer. Immediately after the chime hold down the Command and R keys until the Utility Menu appears.
2. Select Disk Utility and click on the Continue button.
3. Select the indented (usually, Macintosh HD) volume entry from the the side list.
4. Click on the First Aid icon in the toolbar. Wait until the Done button activates, then click on it.
5. Quit Disk Utility and return to the Utility Menu.
6. Select Reinstall OS X and click on the Continue button.

 

Also, see this User Tip: Basic Steps for Upgrading OS X.

If you have backups of your pre-upgraded system then do this:

Install Yosemite or El Capitan from Scratch

 

Restart the computer. Immediately after the chime hold down the Command and R keys until the Apple logo appears. When the Utility Menu appears:

 

1. Select Disk Utility from the Utility Menu and click on Continue button.
2. When Disk Utility loads select the volume (indented entry, usually Macintosh HD) from the side list.
3. Click on the Erase icon in Disk Utility's main window. A panel will drop down.
4. Set the Format type to Mac OS Extended (Journaled.)
5. Click on the Apply button, then wait for the Done button to activate and click on it.
6. Quit Disk Utility and return to the Utility Menu.
7. Select Reinstall OS X and click on the Continue button.

[Permission to use part or all of the above has been granted by Kappy, exclusively, to theratter.]

The above generally only applies to models that did not come with Snow Leopard or earlier pre-installed.