I installed Oracle 8.1.5.0.0 on my PC running Windows NT 4.0 O.S. In SQL*PLUS, under SYSDBA, I created a user as the following:
create user ops$administrator identified externally;
and then:

grant DBA to ops$administrator

Where "administrator" is the user name for my NT 4.0 system.

However, as soon as I attempt to connect to the DB with the username ops$administrator, it always failed. The outcomes are described as the follows:

(1)In the Command Prompt of Windows NT, issue the following command:

C:\>sqlplus /nolog

Then enter the SQL*Plus.

(2)In SQL*Plus, issue the following command:

SQL>connect / as sysdba
ERROR:
ORA-12203: TNS: unable to connect to destination.


I logged on as the super-user administrator, and I am sure that administrator is a member of the ora_dba group.

Who can help me to resolve the problem?