The curse of power mac os. It sounds like the download may not have failed but the installation did so the only thing left that your MBP can boot from is the Recovery partition (see this discussion). Since you don't want to loose all your documents and you don't have a backup to restore from, I can think of a few things to try.
Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing. Turn on your Mac and continue to hold the power button until you see the startup options window, which shows your bootable volumes and a gear icon labled Options. Joined May 21, 2012 Messages 8,919 Reaction score 321 Points 83 Location RI, USA Your Mac's Specs Watch Series 6 (GPS), iPhone 11, iPad Pro 1 12.9' (Wi-Fi), Mac Mini 2014 All have current OS.
Reboot and hold down the option key to see what the MBP sees as bootable. If it's just the Recovery partition, that's where you are. Muzical touch mac os.
If there's a second choice (e.g., Macintosh HD), and it doesn't boot from that, try to reboot and hold down the shift key to start in Safe Mode.
Reboot and hold down the option key to see what the MBP sees as bootable. If it's just the Recovery partition, that's where you are. Muzical touch mac os.
If there's a second choice (e.g., Macintosh HD), and it doesn't boot from that, try to reboot and hold down the shift key to start in Safe Mode.
Getting more extreme would be to get an external drive and Reinstall OS X on it so that you can boot from it and copy over your documents from the internal drive using Setup Assistant.
Wellout Mac Os Catalina
Wellout Mac Os Update
FInally, you could reinstall OS X on the internal. That should get Mountain Lion working again without damaging the rest of your files.
Wellout Mac Os X
Oct 30, 2013 8:56 AM