OK. Then here's what you do:
Internet/Network Recovery of El Capitan or Later on a Clean Disk
If possible back up your files before proceeding.
- Restart the computer while holding down the (Command-Option-R) keys until a globe appears.
- The Utility Menu will appear in from 5-20 minutes. Be patient.
- Select Disk Utility and click on the Continue button.
- When Disk Utility loads select the drive (usually, the out-dented entry) from the side list.
- Click on the Erase tab in Disk Utility's main window. A panel will drop down.
- Set the partition scheme to GUID.
- Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.)
- Click on the Apply button, then click on the Done button when it activates.
- Quit Disk Utility and return to the Utility Menu.
- Select Install OS X and click on the Continue button.
This will completely reformat the drive at which time you can provide a name for the volume like "Macintosh HD." The installer will also create a new Recovery HD. Be sure you have a solid Internet connection. I suggest using Ethernet rather than Wi-Fi because it's more reliable and faster.
If you cannot format the SSD, then it has failed, and it will need to be replaced.