I have lost the use of my MacBook Air through making a password change. The change went through normally - no problem - but when I rebooted the password for my user was refused. (there's only one user plus guest). Thinking I had misremembered the new password I followed instructions to reset the password using Apple ID. Again, all went through perfectly, but again, trying to re-boot failed with the password. I tried the other method proposed: power off, then power on again. Exactly the same - all works and password accepted, but re-booting fails. Literally a dozen attempts with both methods makes no difference. Am I missing something?