This is embarrassing. I have a 2010 iMac that I haven't used for a long time and I can not remember the log-in password. (It does start up.)
I seem to remember that I can start it from the System disk (CD or DVD) by clicking the mouse and holding the mouse "clicked" as I start up the iMac. Then I believe I can get into the operating system and remove the requirement of starting the computer with the Password. Do I have that right? Thanks...
https://osxdaily.com/2010/08/10/forgot-mac-password-how-to-reset-mac-password/