I don't think it is the same problem. It was not rejecting my password. It rejects just when type it wrong (I did to test) with the message "wrong password". When correct, it just show the black screen, like Mint turn off, and then back to login screen.
I could login as a guest, went to system settings, users accounts and unlock my main account to change password. I created account as admin and standard and could login with them. Just my main account was the problem. Well, this until yesterday. Now, I can't login as a guest too, really don't understand why, since I didn't installed/changed anything as a guest. And guest session do not ask for password. It's happening the same: black screen and then back to login.
I tried to use dpkg --configure -a with recovery mode as a root, but it was saying just "can't find dpkg -system-read only" or something like that.