iPhone 4s blank screen despite working speaker and vibration

The screen of my iPhone 4s has gone blank and does not turn on, even by use of a charger. However, it does make noise and vibrate, and sometimes I can hear Siri if I ask her a question, but it takes a while for her to respond. Sometimes, I can also hear my FaceTime calls going off, but I can not answer them. My on/off button does not work, so I will not be able to hold down the on/off button and the home button. Whenever I try to plug my phone in, it makes the noise that it usually makes when I plug it in, but nothing happens. When I was last on it, which was a few hours ago, it was fine and then I turned it off and I have not got it to work since. Also, when I didn't have it plugged in, it got really hot and other times it was cooled off. When I tell Siri to make FaceTime calls, she tells me that she is, but nothing happens. This has never happened to me before, and I would like to know if it has happened to anyone else, or if they have heard about it happening to someone before. Is there any causes as to why this could happen and is there a way that I can help make sure that's this does not happen again? I would like to not have to get a new phone, so does anyone have any suggestions on what I could use to get my phone back to normal? A friend of mine suggested to leave it on the charger for a while, but it did not work and my phone heated up. I hope you guys can help me. :)

It ever happened to my iPhone 5 twice. All I did was left my iPhone until the battery drained off. Then I charged my phone the next day (or when you think the battery is drained already). It worked well afterwards. If it doesn't work for you, you should take to Apple repair shop. Hope it can work for you!