Deleting an Oracle database without connecting to it?
From René Nyffenegger's blog:


  Since 10g, It is possible to drop a database in Oracle 10g with the new SQL statement drop database…
  
  The command gets rid of datafiles online redo log files, controlfiles and spfile…

shutdown abort;
startup mount exclusive restrict; 
drop database;
exit

  
  Requirements:
  
  . database must be closed
    . exclusively mounted
    . restricted 


If you do not have a password, you should still be able to connect from the console, eg:

sqlplus / as sysdba