Hi Guyz,
Its very simple way to get rid of this problem.You just download an app from play store named as
"Back Button (No root)" install it and enjoy the functionality of all buttons like home,back etc.Its actually helpful if your androids menu main menu buttons are not working.
or you can search via browser here it is :-
https://play.google.com/store/apps/details?id=com.appspot.app58us.backkey&hl=en
Thanks,