Ok I finally managed to free some space by removing some files after copying to another drive.
I used rm -r /folder/path command to remove some files that weren't permissions protected.
Didn't think it would be so much trouble to have a filled OS drive (happened to me on Windows and the OS still boot fine).
Now the computer starts as expected before the crash.
I think what happened is I tried to unRAR 15Gb which was split into 15 parts and it was on a NTFS drive so the OS can't write on that.
So instead it wrote everything on the SSD filling it up in the process even though I didn't ask to put data there in the first place.
Thanks to @FrenchPress, @Aravisian, @337harvey which contributed to help me get out of this weird situation I was facing.
At least I learned something today 