At the grub boot menu, type e ( edit )
Go to the line which has kernel... in it, and type e ( edit )
Go to the end of the kernel line and type init 1 and press enter
Then, type b ( boot )
That will get you booted into runlevel 1 with no password needed.
From there, you can add a user and password.
Then, type init 5 and log in as the new user.