Thanks for all your help.
It appears that by keyboard has stopped working for a couple of letters. The letters b and n and the = sign don't echo back. As the letter n is used in the root password as well as my user password, then that explains why it tells me the entered password is invalid.
Also trying to add init=/bin/bash at the end of the Linux line ends up as iit/i/ash which is pretty well useless.
So, I am going to have to find where I can obtain HP service in order to have the keyboard fixed.
Cheers,
Robert