iPhone 4S randomly turned off and will not turn back on

I have an iPhone 4S that randomly turned off. I literally just slipped it into my back pocket and pulled it back out again three minutes later to find that it turned off. Of course, I was very confused, but due to the fact that my top button is broken, I couldn't turn it back on until I had a charger. (Keep in mind, I had 60% battery life.)

About three hours later, I was able to get a charger and it's been an hour since it's been plugged in. However, it shows no signs of turning on or anything.

I've read through similar questions posted on here, but nothing seems to be working/I can't do it with my phone.

Any ideas?

[Extra Notes: My phone has been acting up as of late, by randomly turning off or freezing. But not that often enough to cause a huge problem. However, a couple hours before this happened, I did notice that the wifi was extremely slow on it. Nothing else to report.]