My iMac password suddenly stopped working.
The password I’ve been using to access my iMac for years won’t let me on today. The only message I can get is to change it online but there is no place online to change it.
iMac 27″, OS X 10.10
If you are running Mac OS 10.10, unfortunately its access to iCloud is very limited.
You can try booting the Mac into recovery mode (command-R), and selecting the terminal. Then these commands should help:
If you forgot your Mac login password - Apple Support