forgotten password

Hey rod.hen,
I understand that you can't access your Mac. That is something that can be easily fixed with a few steps.
Resetting your password is easy by restarting your computer and booting to Recovery HD. From there you can open up Reset Password from Terminal and all you have to do is select your user and supply a new password. After that restart your Mac and log in with the new password. For more details, take look at the article below.
Reset the user password in OS X Lion, Mountain Lion, Mavericks and Yosemite
https://discussions.apple.com/docs/DOC-4101
Take it easy

When selecting passwords, make sure it's one that you will NEVER forget AND no one else can figure out.

Old school--- > Print it out & keep in a safe place. A place that ONLY you know about AND never forget.😉 Also helpful when you cannot get pass the log-in screen. 😉

New school---> Get a password manager utility. Highly recommend 1Password which is shareware. Another good password manager utility is Dashlane. Best of all, it's FREE!

Do a Google search for free password managers.