Computer fails to boot up after password change. After new password keyed in, computer also asked for old password. But even when old password supplied, computer just freezes and fails to boot up. What is causing the problem and how can one solve it?

Question

Changed password on MacBook Pro recently. But after password change. Computer ask for old password, thereafter. Even when correctly supplying the old password. Computer system does not boot up and just freezes. What is causing the problem and how can one resolve the issue?

Answer 1

OS X 10.7 Lion, 10.8 Mountain Lion, 10.9 Mavericks and 10.10 Yosemite
Reset Password
Start the computer,then press and hold down command and R keys to start into recovery partition.
When you see the Apple logo, release the keys.
Wait until  OS X Utilities window shows up.
Move the mouse pointer to the menubar at the top and click "Utilities", then select "Terminal"
from the drop down.
Terminal window will appear.
Type in   resetpassword   and press enter on the keyboard.
Leave the Terminal window open.
Reset Password Utility window will open with Macintosh HD selected.
Select the user account from the popup menu box under “Select user account”.
Enter a new password.
Reenter the new password for the user.
Enter a hint.
Click the "Save" button.
Click  in the menubar and select Restart.
Log in.
If Keychain dialog box appears, select “Create New Keychain”.