Why did my password expire?
Windows allows a network or system administrator to create a policy that makes your password expire after a specified period of time (from 1 to 999 days). This is one way to help keep your computer more secure, because it forces you to periodically create a new password. It's a good idea to change your password regularly and to always use a strong password. For more information about strong passwords, see Tips for creating strong passwords and passphrases.