ORA-01031: insufficient privileges as sysdba

I installed Oracle 11g database on window 7 operating system and perform all post installation steps.

Also, set all required environment variable like ORACLE_HOME, ORACLE_SID and TNS_ADMIN in server.

but when i try to login as sysdba.

C:\>sqlplus / as sysdba

ERROR: ORA-01031: insufficient privileges

i got ORA-01031:insufficient privileges.


Solutions:

I did following changes at server level.

1. sqlnet.ora

i changed SQLNET.AUTHENTICATION.SERVICES parameter value from (NONE) to =(NTS)


2. Added user account in ORA_DBA group. 

3. Make sure that the path to the ORACLE_HOME is in your PATH environment variables.


It works successfully after making above changes.