iphone 4s wont turned off by itself

I was in class today when my phone turned off. I tried charging it but it wont work. I cant hold the sleep and home button at the same time because the sleep button doesnt work on my phone. I have been reading some of the responses to similar questions like this stating that your phone could be broken, the charger failed or your cable doesnt work. i know for a fact that my phone isnt broken because i was using it a minute before it turned off. the charger and cable couldnt have failed because i was charging it this morning. please help i dont know what to do.