Do you use ASM, or files on disk? If you use ASM then:
Code:
rman
connect target /;
shutdown abort;
startup mount restrict;
drop database;
exit
or
Code:
sqlplus '/as sysdba'
show parameter dump
show parameter diag
select file_name from dba_data_files
union all
select file_name from dba_temp_files
order by 1;
shutdown abort;
exit
Then go and delete all of the directories with datafiles, then delete all of the dump directories
and if this is 11g delete the directories with the sid name under diag/rdbms.
You should make sure you are deleting the right database first.