FIX your iPhone with a Soft Reset or Soft Reboot if it is not responding or won’t power on. Some other symptoms resolved by this are if the phone wont power on past the Apple Logo or if the phone appears frozen or unresponsive. Sometimes you cannot “Slide to Unlock” or “Slide to Power Off”. Also if the phone does not go back to the home screen. Lastly I have seen this fix issues where apps are crashing or you open a app and it goes back to the home screen.
The same procedure will work on the iPhone 4 / 4S, iPhone 5 / 5S / 5C and the iPhone 6 / 6+ or 6 Plus as its called. Because apple ios is used among other devices it will also help your Apple iPad and iPod.
This is a helpful first step when a device will not wake up, power up, or freezing, lagging and other issues. I have seen multiple times where a iphone, ipod or ipad will not wake up or power up and simply by holding the power key and home key for about 14 seconds, or until the apple logo pops up. Has worked most of the time unless your battery is completely drained. Also this wont work if your Home button or Power button are defective. Below is the link to Apple’s KB article.
Apple has a Knowledge Base article about this