MacOS – MacBook Air is stuck at “Downloading Additional Components”

I don't believe a Mac can be locked to the point where you cannot even install a fresh OS. That would require a locking at firmware level, and I don't believe the MacBooks offer this option.

You should be able to restart, with the option (alt) key pressed, so that you get into the boot screen where you can choose to start up from the recovery system, and then re-install OS X from it, all without needing a password.

Oh, I see you also asked here: Resetting password for Macbook There, you mention that you were able to get to the rescue screen with Cmd-R. So, why can't you re-install OS X then? It's offered as an option there, isn't it?

Reset the SMC:

1) Power down the system
2) Unplug all cables except Magsafe
3) Hold down left Shift + Control + Option + Power button for ~5 seconds
4) Boot machine up

This usually solves issues when certain hardware devices on the device itself aren't responding, especially when multiple do not work.