drop the whole datase

@C

 could you please anybody let e know how to drop the whole database.

I have trie using the follwoing,

dropdatabase.sql file has the follwoing commands

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

and i tried running from command prompt as

C:\>sqlplus  username/password @C:\dropdatabase.sql

but i got the following error

ORA-01031: insufficient privileges
ORA-01031: insufficient privileges
drop database
*
ERROR at line 1:
ORA-01586: database must be mounted EXCLUSIVE and not open for this operation

pls tell me the correct steps to drop the database.

Thanks