Q: Suddenly my Ipone 4 has no sound

Reset the device:

Press and hold the Sleep/Wake button and the Home button together for at least ten seconds, until the Apple logo appears.

If that doesn't help, tap Settings > General > Reset > Reset All Settings

No data is lost due to a reset.

Am using Iphone 4s since 2013 but last few month getting sound problem,even i reset all setting and upgraded IOS 7.1.2 but still same issue.let me know any setting require.looking forward help from all.thanks in advance.

Make sure that you have gone through all of the steps in this article.

If all else fails, create a backup of the iPhone to either iCloud or iTunes and then restore the iPhone.  After restoring, you'll want to temporarily set up the iPhone as "a new device" to see if you're still having the same issues under default settings.  If the issue seems fixed at that point, attempt to bring back your backup.  If the issue comes back with the backup, then the backup is corrupt and you'll need to set up as new.