I just spent several hours fighting past this.
If your windows operating system working directory
has a .ora file in it, it will not let you log in
using sqlplus / as sysdba
Sorry, but that's pure b.s. Show us the proof.Catch a plane to Addis Ababa, Ethiopia and I'll be glad to sit you down and show you. I'll even pick you up at the airport!
You can connect to the database without giving a password if the user under witch you logged to the operating system is a member of the ora_dba under Windows or dba under Linux/Unix. otherwise you will have to provide a password so that oracle can authenticate you using the password file.