In Oracle when password is expired you will get following error:
ORA-28001: the password has expired
This is because password have reached 180 Default limit for Password life time.
Solutions:
1. Connect to database using sys users.
2. Execute the following query
Sql > select * from dba_profiles;
the output of this query will be like.

Here PASSWORD_LIFE_TIME field is responsible for expiring of password after 180 days.
3. execute following command to disable this feature:
Sql> ALTER PROFILE DEFAULT LIMIT PASSWORD_LIFE_TIME UNLIMITED;
4. Now crosscheck for disabling of this feature.
Sql > select * from dba_profiles;

The value in PASSWORD_LIFE_TIME has changed to unlimited. Now password will never expire.5. Now change the password of locked user and unlock using following.
sql> alter user [user_name] identified by [password];sql> alter user [User_name] account unlock;
6. Crosscheck by value of accout_status field in dba_users view.
sql> select username,account_status from dba_users;
The value of account_status filed should by “OPEN” for corresponding user.