ORA-28001: the password has expired

Crosscheck by value of accout_status field in dba_users view.
sql> select username,account_status from dba_users;

Execute the following query

Sql > select * from dba_profiles;

the output of this query will show, Default Password expire lifetime 

PASSWORD_LIFE_TIME field is responsible for expiring of password after x days.

execute following command to disable this feature:

Sql> ALTER PROFILE DEFAULT LIMIT PASSWORD_LIFE_TIME UNLIMITED;

Now crosscheck for disabling of this feature.

Sql > select * from dba_profiles;

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;

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.