Just check whether the OS userid which u r using to log into that m/c belongs to ORA_DBA group.
I assume that u r on the server and as I recall from ur previous posts .
That u r on Oracle8 so Internal user is very well there.
Last but not least u have the option of doing either of the two things as I mention below.
1. Stop the OracleService and delete that using Oradim -delete -sid.
Then recreate the service using Oradim utility where u have the option of providing the password for internal ie intpwd parameter.
But before doing that make sure u delete the Pwd<sid>.ora file.
2. Stop the service and delete the password file Pwd<sid>.ora.
Then recreate the password file using Orapwd utility.
The syntax for both the utilities can be obtained from the command prompt.