It is common with the Vodafone 785 to suddenly go mute. Neither ringing, nofications tones nor outputting sound for video playback? This is normally owing to a corrupt cache and clearing the system partition normally remedy the issue. The Vodafone VF785's cache partition can be cleared in one of two ways.
Method 1 - easy buy may not be as straight forward.
1. Download the app called "App Cache Cleaner" from Google Play Store
2. Run it and compute and clear all applications cache
3. Reboot the VF785 and sound should be restored to all
1. Press and hold both the Power button and the Volume button until the Vodafone 785 power on and go past the (powered by Android) screen to a reddish menu - the Android System Recovery menu-------------
2. Scroll using the Volume Down key and highlight "Wipe cache partition" - WARNING! not the "Wipe data/factory reset"
3. Confirm selection using the Power button (simply short press it)
-------------the "Wiping commences soon after the selection....
4. With "Reboot now" highlighted - following the wiping, short press the Power button to select and reboot/restart the phone.
This method as well should ensure that data is restored after clearing the cache partition in this way