GeorgeM

I am Replying to myself here so that it may help someone.

I had to rebuild my machine BUT it allowed me to experiment and this is what I found.
If you have the Guest account disabled then the computer is inaccessible. BUT if the Guest account is enabled (I set it up with no password) YOU WILL be able to sign on using the Guest signon.
If you then try to go to the USER ACCOUNT section, access an account it will prompt you to sign on with an administrator signon. Do so, using the correct password (all passwords and signons are intact). You will get in. If you RESTART your computer or logoff and try to signon as admin you should be successful going forward. ALternatively, you could set up new accounts and delete old ones.
Hope that helps someone. (Remember: Enable the Guest account before applying the the registry "DontDisplayLastUserName" change).
I realise that there maybe other solutions but this worked for me. If anyone has a better solution please share it with us all.