Why does my iPhone come up with the apple logo and freeze

I have had my iphone 4s since December 2015 it was brand new, but over the past 6-8 month I have been having muiltiple problems with the iphone I use to be able to just restart the iphone with the power button and the home button but the power/lock button no longer works and the iphone gets hot whilst on FaceTime and after 5 ,mins on FaceTime it disconnects it's self from my wifi whilst my iPad still works perfectly, then I try to sort the wifi by turning it on and off in wifi on the settings but it just freezes my phone and the screen becomes darker and adventually turns off then appears with the apple logo normally it would just kill the battery which takes 2-3 hours but today the screen has gone really I'll still showing the apple logo but it won't do anything. Thank you in advance x