My IPhone froze and turned off and won't turn back on?

I was texting on my IPhone 4 when I looked away, and when I looked back, it was frozen on the lock screen. I let it sit for a couple of minutes, but then it turned itself off and I think it restarted because the Apple logo came up, but then it disappeared and I haven't seen any signs of life since. I had at least 75% battery, and I tried to reset it with the home+lock screen at least half a dozen times, but to no avail. If anyone can help, it would be greatly appreciated.

Added (1). I plugged it into my computer and opened ITunes, but it didn't recognize my phone being there.

Try plugging it in your computer and connecting it to itunes? It might be in dfu mode, google how to get it out of dfu mode x

I would try taking it apart taking the battery out putting it back in and plugging it into the charger. I don't know how but they can be taken apart

Did you accidentally get the phone wet? The battery may have fried. Pour white rice into a ziplock bag put your iphone in there and let it sit overnight. If this didn't work take it to a phone tech.

This happened to my brother twice. All you have to do is hold the home + lock buttons for a really Really long time. Maybe like 30 minutes

Hold the home and lock button down. It sounds stupid, but its a real life savor.