iphone volume gone missing after restart,reset and opening an apps
i have 2 issues here. firstly, my iphone volume suddenly gone missing after restart, reset and opening an apps. second, after sliding off power and the iphone sudden turn back on by itself. however, i followed those steps to fix the volume bar missing by cleaning the dust inside the charger socket and headphone socket but didnt work. I tried restart/reset 4-6 times and the volume appear but after opening an apps like spotify, music the volume came back disappeared.. please help me how to fix these problems?
iPhone 4S, iOS 8.2