ORA-01031: insufficient privileges whiling logon through / as sysdba

Here we have 2 solutions

a)       In sqlnet file in network folder  we should have

When it is set to NTS, which should only be set on Windoze, it allows users to be authenticated using Windows NT native security. What this means is that by setting SQLNET.AUTHENTICATION_SERVICES to NTS
and a creating a role called ORA_DBA with your user in that group you should be able to log in to oracle without supplying a password. (connect / as sysdba)

b)        Or check weather is there  password file or not .  by giving sysdaba privilege to
           Sys . if u get any error 

create pwd file using orapwd utility  with not giving the “nosysdba=y”  parameter