SQL> conn system/oracle as sysdba
Connected.

[B]bcoz of sqlnet.ora in "authentication method is "NTS".[/B]
SQL> /
SP2-0103: Nothing in SQL buffer to run.
SQL> conn system/oracle as sysdba
ERROR:
ORA-01031: insufficient privileges

Warning: You are no longer connected to ORACLE.

[B]i was change authentication method on sqlnet.ora "NTS" TO "NONE"[/B]
SQL> conn sys as sysdba
Enter password:
Connected.
SQL> grant sysdba to system;
grant sysdba to system
*
ERROR at line 1:
ORA-01109: database not open


SQL> alter database open;

Database altered.

[B]SQL> grant sysdba to system;[/B]
Grant succeeded.

SQL> conn system/oracle as sysdba
Connected.
SQL>