2012 Macbook Pro model A1278 No operating system.

Hello RUBITRON55,

Thank you for reaching out to Apple Support Communities.

If your device is unresponsive you may have to restart our device and attempt the install again: These steps can help you reinstall macOS:

"Other macOS installation options

When you install macOS from Recovery, you get the current version of the most recently installed macOS, with some exceptions:

• On an Intel-based Mac, if you use Shift-Option-Command-R during startup, you might be offered the macOS that came with your Mac, or the closest version still available.
• On an Intel-based Mac, if you use Option-Command-R during startup, you might be offered the latest macOS that is compatible with your Mac.
• If you just erased your entire startup disk, you might be offered an earlier compatible version of macOS.
• If the Mac logic board was just replaced, you might be offered the latest macOS that is compatible with your Mac.

You can also use these methods to install macOS, if the macOS is compatible with your Mac:

• Use Software Update or the App Store 
• Use a bootable installer"

More details can be found here: How to reinstall macOS

If the issue persists, can you provide a few more details? What happens when you attempt to create a bootable drive? Also, which macOS version did you previously have?

Cheers!