Linux Mint Forums

Is this an installed Mint?
Seems so...
It's really simple and the solution shows that if someone has physical access to the computer security is none
Boot into recovery mode
type passwd + username (enter)
Type new password twice
Done
Type " exit " or reboot - this is the only way to leave recovery mode

When you turn on your computer, select 'Recover Mode' from the GRUB boot menu...
This will start Mint in a passwordless 'root' shell - BE VERY CAREFUL!!!!
Type in passwd <username>. (Set your password.)
Type reboot
You should now be able to log in with the new password you just set.

Well you can only change password for an existing user - that's not surprising.
As you have changed password you now know both user name and password and should be able to log in
Note that passwords are case sensitive ans user names always "small letters" not KApital ones
If not we have to think of something else
Can you log in at all? Failsafe terminal, whatever...
Is there more than one user and if so is this the super user (the one with sudo power)?