System account locked, insufficient privileges to log in as sysdba
The windows user account belongs to Administrator and Ora_DBA Windows
  groups.


Double check this, because you get the above error, when you are not a member of the ora_dba group.

Check %ORACLE_HOME%/network/admin/sqlnet.ora for the following line:

SQLNET.AUTHENTICATION_SERVICES=(NTS)

If it is set to NONE, that disables logging in with / as sysdba, but would result in a ORA-01017: invalid username/password; logon denied error.

Finally, SYS password is stored outside the database, in a file, on Windows it is %ORACLE_HOME%/database/PWD%ORACLE_SID%.ora. You can recreate it (give new SYS password) as:

orapwd file=%ORACLE_HOME%/database/PWD%ORACLE_SID%.ora force=y

After that, you can should be able to log in with the given password as:

connect sys/password as sysdba