Correct password NOT accepted / login not possible at all

Forgot Your Account Password

For Lion, Mountain Lion, or Mavericks

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

When the menubar appears select Terminal from the Utilities menu.

Enter resetpassword at the prompt and press RETURN. Follow

instructions in the dialog window that will appear.

Or see:

Reset a Mac OS X 10.7 Lion Password

OS X Mountain Lion- Reset a login password,

OS X Mavericks- Solve password problems,

OS X Lion- Apple ID can be used to reset your user account password.

For Snow Leopard and earlier with installer DVD

Mac OS X 10.6- If you forget your administrator password,

OS X- Changing or resetting an account password (Snow Leopard and earlier).

For Snow Leopard and earlier without installer DVD

How to reset your Mac OS X password without an installer disc | MacYourself

Reset OS X Password Without an OS X CD — Tech News and Analysis

How To Create A New Administrator Account - Hack Mac

If you need to reset the Keychain, then see:

Assuming that you are using a recent build of OS X, go to /Applications/Utilities and launch the app called Keychain Access. Go to the Window pulldown menu and select "Keychain First Aid". Enter your password, set the radio button to "Repair", and click "Start".

If you want to preserve the data on the startup drive, and it's not already backed up, you must try to back up now, before you do anything else. It may or may not be possible. If you don't care about the data, you can skip this step.

There are several ways to back up a Mac that is not fully functional. You need an external hard drive to hold the backup data.

1. Boot from the Recovery partition or from a local Time Machine backup volume (option key at startup.) Launch Disk Utility and follow the instructions in this support article, under “Instructions for backing up to an external hard disk via Disk Utility.”

2. If you have access to a working Mac, and both it and the non-working Mac have FireWire or Thunderbolt ports, boot the non-working Mac in target disk mode. Use the working Mac to copy the data to another drive. This technique won't work with USB, Ethernet, Wi-Fi, or Bluetooth.

3. If the internal drive of the non-working Mac is user-replaceable, remove it and mount it in an external enclosure or drive dock. Use another Mac to copy the data.

My feel from 20+ years of dealing with Mac problems is that very possibly I, for whatever reason, have encountered an incomplete OS update. None of the suggestions above truly apply. As noted above, I did try several but no improvement.

Do you think the best solution is to just download the 10.9.2 update from Apple Support, run it locally and see if all comes out well? (I found a link to that: http://support.apple.com/kb/DL1725.)

Roughly the same problem but with a single MacBook Pro 15" Retina. Post 10.9.2 update, it asked for password when restarting during the update process. It had not been set to ask for password previously. And it wasn't accepting what I knew to be the password (My system password hasn't varied in going on 20 years.) I was able to reset the password via the Apple ID password recovery process (and set it to the same password). Based on the above discussion, I tried Keychain First Aid but it found nothing amiss.

At first, the System Prefs folder opened as a blank window. After another restart, it opened normally but was frozen. After a couple more restarts, it started working.

At present, I am able to log in and get my desktop. However, most applications either won't start or stop responding rather quickly. As soon as I'm logged in, I get a succession of six error messages wanting a password. "The wording for each is xxxxx wants to use the "Local Items" keychain. Please enter the keychain password." The fill in words are talagent, identyservicesd, CalendarAgent, com.apple.internetaccounts, AddressBookSourceSync and com.apple.iCloudHelper. I have never set a password for the Keychains. My system password doesn't work for these messages. Either clicking cancel or OK three times takes me to the next error message. After 18 clicks, I'm back to the first message to start all over.'

Looked at the iCloud box in Systems Prefs and it is an oxymoron. On the left, it's normal, e.g my account name, button for details and button for Sign Out. But, above the list of apps, it states "enter your password to continue using iCloud. Verify the Apple ID password for sactobob@mac.com." and is followed with a box Enter Password. On entering the password, you see the dark gray gear spinning -- forever -- and you eventually click Cancel.

Any ideas on repair of this situation? I think it has something to do with whatever interacts with iCloud. Why? Because anything related won't work. Pages is not aware of its cloud documents, Mail.app prefs > accounts wants me to start an account while one can plainly see dot mac email collected pre-update.

What backups do you have?