640/735 Sounds Disabling

[Windows Central Question]

I have 2 Lumias - 640 &735. Both run W8.1 and suffer the same problem. I lose sounds, the most important being incoming call alert. I know they have disabled as the keyboard key clicking disappears.
The way to remedy this is a hard boot but this is becoming tiresome and I'm missing calls when I'm not aware.
Why is this happening and what is the cure, please. Many thanks if you can help.

 

[abhishek singh21]

have you tried a soft reset? you could do that by holding together volume down+power key until phone reboots.

Also i would insist that you upgrade both your devices to windows 10 mobile using the upgrade advisor app.

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