When I tried to log in as SYS with "SYSDBA," it gave me insufficient privileges.
Check to make sure your windows user is part of the ORA_DBA group. You may need to ask your Sys Admin to check for you. If your user is part of the ORA_DBA, you automatically have the SYSDBA rights.
Note: if your Windows user is a member of Administrator group in Windows, then if you install Oracle, the user name automatically gets added to ORA_DBA group.