iMac lock screen password not working

[amg7468]

I know my Apple ID & Password and they both work for every purpose on my iMac except the lock screen. If I swipe my mouse in a certain way (and I'm not exactly sure which mouse gesture it is) but it locks my screen and demands a password be entered to unlock it. However, it doesn't accept my normal Apple password, the same password I use to install things or for purchases etc. I have to do a hard reboot and it logs on as normal. I would appreciate any help with this.

 

[hfg]

Is your iMac boot login the same as your AppleID password?

The system password (boot) is what the screen lock is looking for, and can be changed in SystemPreferences/Security/General or on your SystemPreferences/Users page.

You might try re-entering your boot password on the security page just to see if that fixes it.

 

[amg7468]

I tried the system preferences, both security and user accounts and it let me enter my known password as the current password, then enter it again as the new and verify passwords with out any error messages or confirmation messages. It just returned to the security or user account window respectively without a whimper.
I then locked the screen again but the password didn't work. After a few tries it gave me the chance to change it using my Apple ID, so I went through that process and it still doesn't work.
All that happens when I enter the password on the lock screen is the screen jumps a little bit then stays put with the password highlighted, but no error message. It isn't very intuitive!!

 

[hfg]

Possibly a "permissions" problem ... boot into the recovery mode and use the DiskUtility found there to "Repair Permissions" on your boot disk.

There is also the "fix-all" PRAM reset, but I don't think that is your problem, but it doesn't hurt to try it. That is the first thing Apple Care will have you do, then SMC reset, then reinstall OS X non-destructively from the Recovery Mode (I would have a full backup before doing anything such as this )