Oracle on Windoze

I'm a *nix command line type DBA who has next to no experience directly supporting
Oracle on Windoze.
I get logged onto the DB server system as "administrator" & this account supposedly
was used to install Oracle.
However when I open up a command window & invoke SQL*PLUS and then / as sysdba
The error message reports I have insufficient privileges.

How do I get into this DB as "SYS"?

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