the sentence which you've seen is an error sentence. here is its code:
$db = db_open(DB_TYPE, DB_SOCK, DB_HOST, DB_PORT, DB_USER, DB_PASS, DB_NAME);
if (!$db)
error_503('ERROR_TITLE', lang('ERROR_DATABASE_OFFLINE'));
I haven't changed anything like password,db name, username or anything else. But it got offline..