As I was on face time with my mate and I locked my screen, suddenly my phone went black I pressed the home button several times but it didn't work.
My lock screen button hasn't been working for 3 months I was scared because I thought it was permanently damaged the notification sounds worked, but I needed my phone especially because its 3 hours until the new year.
So I suggest draning your battery out fully and plug it to a computer and it will switch on !