Start up disk is locked

You want to install macOS on a freshly erased drive. Is that correct? If your model is from Late-2011 or later, then do the following. You will need a fast, working Internet connection, preferably, Ethernet. Upon completion this will install the original version of macOS that came when the computer was new from the factory - a Factory Reset.

Internet/Network Recovery macOS on a Clean Disk

     If possible, back up your files before proceeding.

1. Restart the computer. Immediately, at or before the chime, hold down the (Command-Option-Shift-R) keys until a globe appears.
2. The Utility Menu will appear in from 5-20 minutes. Be patient.
3. Select Disk Utility and click on the Continue button.
4. When Disk Utility loads select the target drive (out-dented entry w/type and size) from the side list.
5. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
6. Set the partition scheme to GUID.
7. Set the Format type to APFS (SSDs, only if installing Mojave or Catalina ) or Mac OS Extended, (Journaled.)
8. Provide a volume name, usually "Macintosh HD."
9. Click on the Apply button, then click on the Done button when it activates.
10. Quit Disk Utility and return to the Utility Menu.
11. Select Install OS X and click on the Continue button.

Please read Writing an effective Apple Support Communities question. We are here to help. We are all users. We are not mind-readers nor clairvoyants. We only know what you write down and tell us. Be specific and thorough. Try to write clearly. Think about what you want to say before you write it down, then re-read it to see if it makes sense. We need the following at a minimum:

• What specific product model do you have? Avoid just saying, "iPhone or Mac," because that doesn't describe it uniquely.
• Tell us the version of iOS or Mac OS that you have installed on your machine.
• Provide a short but complete summary of your question, problem, or issue. (No complaints, please.)
• Give us all the details of your question, problem, or issue. Make your descriptions clear and precise but don't be wordy. Like Joe Friday used to say, "Just the facts." Be sure you provide any other details that we should know.
• Detail what you have tried, so far, to solve your problem even if it's "nothing."

If English is your second or third language, please let us know. Perhaps you would be better served by posting in your native language. If you do, then understand that getting a reply may take more time. Most of the helpers are native English speakers but some of us are bi- or multi-lingual.

FYI: These are user-only communities. This is not Apple Support. if you need to contact Apple Support, then contact product and tech support: Contacting Apple for support and service includes international calling numbers.

The Apple Support Communities only provides help for users of Apple products. Apple does not read theae forums. If you wish to provide feedback to Apple, then go to Apple Feedback. Thank you for your understanding and support.