How to use Public Database Link when connect as SYSDBA

DB VERSION: 10.1.0.4

(Database was cloned FROM ABC)

SQL> create public database link ABC
  2  using
  3  '(DESCRIPTION=(ADDRESS=(protocol=TCP)(host=ABC123)(port=1521))
  4  (CONNECT_DATA=(SID=ABC)))';

Database link created.

SQL> select sysdate from dual@abc;
select sysdate from dual@abc
                         *
ERROR at line 1:
ORA-01017: invalid username/password; logon denied
ORA-02063: preceding line from ABC

No problem when connect as SYSTEM or other users.

SQL> connect system
Enter password:
Connected.
SQL> select sysdate from dual@abc;

SYSDATE
---------
21-FEB-12