Speaker on Nokia 720 is not working any more. no ringer, no music just no more sound. However headphones are ok.

read this forum.... there are two or three different ways to solve it.
http://discussions.nokia.com/t5/Lumia/no-sound-from-my-nokia-lumia-720/td-p/1935826

I would suggest contacting Nokia Care and getting the device repaired or replaced under warranty.

I ran into this same problem with my Nokia 900. It happened right after I plugged and unplugged a headphone into the headphone jack, so I suspect Nokia ships with a defective headphone jack sensor, because this happened with the second phone after I returned the first one and got a new one. (Note to self, don't plug a headphone into a Nokia phone). I am able to temporarily get around the issue by going to the dialer and calling ##634#, then going to the audio loopback diagnostic and starting the loopback for the phone and choosing loudspeaker. This does not last permanently, so I have never found a solution to the issue, other than using blue tooth or speaker phone.

Have you synced your Nokia Lumia to a computer, if so, you can delete all the contacts from your computer. Else you can go to Sign In , log in with your Windows-account, go to 'People' and select all the contacts you wish to delete (in your case all). Next click 'Delete Selected'. This should solve your problem, good luck!

try other mmc

If this isn't due to your phone being dropped in water, try doing a soft rest. To do this........Hold the "down volume" and "power button" at the same time for ten secs, until it vibrates, then let go of those buttons. The phone will now reboot. This will not erase any of the content on your phone (i.e., games, contacts list, programs, etc.)

Hope this helps. :)

#Option 1, Hard Reset NOKIA LUMIA 720 with software menu:

1. Turn on the NOKIA LUMIA 720
2. Go to Menu Setting > Setting
3. Choose About and choose Reset your phone

#Option 2, Hard Reset NOKIA LUMIA 720 with Hardware Key Button:

1. Turn off NOKIA LUMIA 720
2. Press and hold together Volume Down Button + Power Button until LCD show exclamation mark icon
3. Now release all number 2 buttons.
4. Press one by one continuously:
   1. Press and Release Volume Up Button
   2. Press and Release Volume Down Button
   3. Press and Release Power Button
   4. Press and Release Volume Down Down
5. If the step finish, the NOKIA LUMIA 720 will do the hard reset or factory format by itself.
6. Wait until it finish to format, then we will need to setup like new again.

A friend of mine had the same problem. The 3.5mm headphone socket was playing up, thinking they were still plugged in. She plugged headphones in and give it a push and a wiggle, then took it out and now it works. Give it a try.

The loudspeaker is what the ringer uses as does the music, the inner speaker is used for hearing calls. Sounds like your inner speaker is faulty, check with where you bought it and it may be free to repair if its still under warranty (usually 12 months from date of purchase)

It seems the speaker or buzzer is already busted and need replacement.sometimes it happens when the phone drop on the ground or been playing sounds fully loud for a long time.parts is available in any mobile service shop near you.