Hello.
Is there an error message after trying to log in?
Some clue if password or username is incorrect?
Did you use upper/lowercase letters?
Did you use special characters in your password at setup?
Maybe some that are not there at the time of logging in?
(e.g. I faced once an issue with an encrypted Mint, where I set my initial password with german keyboard set, but after rebooting the y and z were switched (as in english keyboard settings), took me a while to realize…)
Maybe you could boot up a live system, mount your harddisk and look up your username in /home
I actually didn’t make a complicated pass… it was just 3 numbers nth more, and the same for username of 2 letters as u see in the pic above.
anyway I reinstalled the sys as the only quick solution left for me
Sometime ago had the same thing happen with Ubuntu Mate in VirtualBox. I used my normal password and no it would not except it. So reinstalled and used simpler password, then changed it back to my normal Password and it excepted it, after updating it of course. Linux can sometimes be a pain, like any other operating system in the world.