Because i'm curious about password recovery,i had the same problem before. I couldn't open a computer that hadn't worked in two years (Without password),i did a lot of things without success.
I did not record my login password, and I have many passwords, I do not know which is the password of this locked computer.I have a Mac, an iPod,so I haven't opened on this computer for 2 years.
Do you use Google? It stores passwords for you and you can look it up. Click on the three dots in the upper right corner and go to settings. Look up auto fill and say passwords.