you do not state your version.
However, make a new passwordfile would work.
otherwise, connect at command-line of the host through telnet or at the terminal (not through a client) and use:
SQL*Plus: Release 184.108.40.206.0 - Production on Thu Jul 10 10:50:14 2003
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Oracle9i Enterprise Edition Release 220.127.116.11.0 - 64bit Production
With the Partitioning and OLAP options
JServer Release 18.104.22.168.0 - Production
sid:username> connect / as sysdba
sid:username> show user
USER is "SYS"
you can lead someone to something but they will never learn anything ...