ERROR: ORA-01031: insufficient privileges
since I'm the only one using the computer I'm assuming it's the same as "Administrator"


That's not enough to be an Administrator. 

Make sure that your user belongs to ORA_DBA OR ORA_&lt;%ORACLE_SID%&gt;_DBA OS group on Windows. 

As well check the value set for SQLNET.AUTHENTICATION_SERVICES parameter on sqlnet.ora(%ORACLE_HOME%\network\admin) file. NTS should be included in the value. 

SQLNET.AUTHENTICATION_SERVICES = (NTS)