Ubuntu 16.04 – Reboot after "sudo mv / *", my computer does not recognize my credentials anymore

Hi everyone, i'm currently trying to get my computer out of comac.
I've tried two options:

  • a- try Ubuntu without installing
  • b- install Ubuntu

a- try Ubuntu without installing

To remedy my situation, I put Ubuntu 16.04 on a USB key and, in any case, I made the option to restart on USB drive and everything is fine so far. The problem is that when it comes time to open a user's session, my computer no longer recognizes my credentials, it sends me back:

invalid password, try again

dude, my broken computer is making fun of me now!

maybe I moved my identification information with my sudo mv / *the command. How to restart Linux if I can not connect?

I have seen web tips on "alt + ctrl + f *", but even here, my system asks me for my credentials.
The problem is that I can not connect so I am bluffed behind the connection interface. *

b- install Ubuntu

Also note that using "install ubuntu" leads me to a blank screen with underline, the majority of solutions on the web are talking about using a tty to make some commands, but then again, I'm stuck on the connection interface.

How can I restart my system?

Note: I'm currently trying to access GRUB but I do not know where it really stands, people are talking about "hold shift on the bios menu", okay, I'm looking for . I guess the BIOS menu is on esc => f10 -on my computer. perhaps he is elsewhere.

Any hint would be great,

thank