Phone is working suddenly display is not showing

Hi I am having Samsung Note 2 , is was working perfectly and my son was playing on it. It's battery goes to zero and if switched off. Then I charged the phone overnight and when I switched on the pH in morning display is not coming although calls are coming but no display.kindly help.

I showed it to mechanic and then switch it on with some device not the pH battery and told me that it's display gone. Still it's puzzled me how come ph display gone just charging it.