Mac mini won't start in any mode. Looks to be some kind of disk failure We got a strange trouble. My sister has a mac mini, and it for same reason stopped working. Tried to restart it in any possible mode. Can't restart even from a bootable USB stick with mac OS, making it impossible to be erased or fixed. Only mode that started is single user mode ( command  line ) where the disk could not be fixed. But, I saw that in single user mode, I can list directories and files. So, the disk looks to be working.

What makes it even more bizarre, is that when plugged this disk as a external disk on another mac computer it restarts immediately and shows the black screen of death. ( that one that says "this computer restarted because of a problem").

Is this a physical disk failure? Any ideas? Never seen anything like that.
Right after the root# prompt, enter the following:

/sbin/fsck -fy


Press the Return key.

Background: You can repair a drive by using the fsck command. Fsck stands for File System Check (the name is sometimes referred to as File System Consistency ChecK); it can be used with various optional parameters.

It will take a few minutes. 

In the end, if your drive was OK, the screen will say “The volume (name of your hard drive) appears to be OK”. If any repair was made, you’ll see the prompt, “FILE SYSTEM WAS MODIFIED”. Then, you’ll see the root# prompt again.

Right after the root# prompt, enter the following:

reboot


Press the Return key. Your Mac should restart normally. Let me know how it goes.