This is the query we run to populate the 'Object Name' list.
select object_name from sys.all_objects where object_type in ('TABLE', 'VIEW', 'SEQUENCE', 'PROCEDURE', 'FUNCTION', 'PACKAGE', 'TYPE', 'SYNONYM')
and owner = :1 order by object_name
You have probably selected a schema for which there are no tables, views, sequences, or PL/SQL objects that you have SELECT access to - hence it doesn't appear in YOUR all_object's view.
Run that query in a SQL Worksheet to confirm that indeed, 0 rows are selected.
Then go ask your DBA to grant you privs such that you can work with those objects.