The Ubuntu wiki can help you with a password reset. I would look closely
at letter case, Linux is case sensitive.
I would think an install yesterday could have the fastest easiest cure
in a re-install. I would consider a password I could easily type in
without errors. In all honesty secure passwords are only important in
business or gov. My password is easy to put in and is not considered
better than poor but no one allowed in my house is anything to worry about.