At IMAC sign in screen but for the first time IMac will not accept my password. I have tied six times. No go. Rebooted. No go. Did three shut down and restarts. Still will not accept my password which I have used for 14 months.

Since I did the last IMAC update the computer automatically restarts, without my command? Each time I would sign in my password and the system returned to where I was working??? Tonight it restarted in the middle of my work BUT it will no longer accept my password, which is the same password I used to sign in for this discussion.

I have tried entering the password “six” times hoping to get instructions to reset password. rebooted three times, and have done three shut down and restarts. System always returns to the sign-in screen but still will not accept my password.