In my previous post i have explained a laborious method to the sound (drums) back. But it failed to play my sound once my ubuntu got updated.i tried the previous steps again but failed.
Here got the new easiest and quicker method to get login/startup sounds back.
->install "dconf editor"
->there you can find theme-name (by default it's value will be "freedesktop").
->change it to "ubuntu"(don't forget all are lower case)
-> then logout and login
->that's it you can hear your drums back.