The back key is not working in lumia 720

[WPCentral Question]

Hi All,
I m using a Lumia 720. And its been six months. And suddenly the keys at the bottom(the back key, home key, and the search key) is not working for a particular period of time. There is no response for almost two to three days and after that, it behaves normally for a week and the same problem continues.
Can you please help me what might be the issue and whats the solution??
Thanks in advance

 

[anon(7900571)]

Hey can you please post your OS and firmware version , and try a soft reset by holding volume down + lock button at the same time until your phone vibrates and reboot itself (ignore the black screen to power off the phone ).