I Don't have PFILE or SPFILE just have a backup of init.ora and database is down
yes, backup of your parameter files is a smart thing to do, like backing up your database is a smart thing to do. If you still have an alert log file of your database, you can extract the parameter settings from there and use them to create a pfile using good old vi or whatever simple text editor you like.
Most important parameters are 


instance_name 
db_unique_name
control_files


Once your parameters are complete, you can verify them by trying to startup the database.

ORACLE_SID={YOUR_ORACLE_SID}
. oraenv
sqlplus / as sysdba
startup nomount pfile={your_pfile_full_name}


If this succeeds, your parameters are good enough to start an instance. Now see if your control_files parameter is OK:

alter database mount;


if your database mounts, you have access to your control file[s].

alter database open;


you could be back in business by now.
Since it is smarter to use an spfile, now is the time to create your spfile:

create spfile from pfile='{your_pfile_full_name}'


This creates the spfile for this instance with the default name in the default location (${ORACLE_HOME}/dbs/spfile${ORACLE_SID}.ora). Shutdown your database and start it without specifying a pfile or spfile. It should select the just created spfile and give you back your database as it was before.