Dear Mr. Shiv,
As per the above information I assume that,
Operating system is Aix.
Database is DB2
You can try following,
Login with db2<sid> user at OS level.
Run the command 'db2start' to startup the database.
After starting up the db,
go back to user '<sid>adm' and give 'startsap r3'.
In case problem persist, you may try by a reboot of the Operating system to start all daemons properly.
Kind rgds,
Ashwin Mane