Locked out of user account (Macbook)

Hi Everyone

I’ve used the same password to access my MacBook Retina 12” for years. For no apparent reason today it won’t accept it. I know it is correct as it is the registration plate number from an old car (that only I know btw).

I’ve looked online for solutions but none seem to match up. One approach is to open the MacBook in recovery mode (shut down, restart holding command+r) but that just opens my accounts page as if I were just restarting as normal. I’m baffled. Any suggestions gratefully received.

Thanks

Mr C.