hi Aruva,
Was there any activity carried out before you started facing this issue. And one more thing is did you have a dbm studio installed try to connect to DB using it.
Also whats the output of dbmcli -d <dbsid> -u control,<password> db_state.
also can you verify your db SID & are you able to login with SDB user.
Let us know the details.
Regards,
ram