I've been beating my head against the wall trying to reset the password for an Oracle 8.1.5 database. I've tried the following and this seems to be the consensus on how it should be done.
You have to go to server machine and logon as OS user
that has installed Oracle (it belongs to DBA group or something like this).
After that you can
svrmgrl>connect internal as sysdba
Now try to change the SYS password:
svrmgrl>alter user sys identified by manager;
If this runs successful you will be able to logon
svrmgrl>connect sys/manager as sysdba
However I still get prompted for a password! I'm logged in with an account that is a domain admin and a member of the ORA_DBA group.