^And if that doesn't work, and I'm talking worse case senerio here, you have to put your iPhone into recovery mode.to do so you must follow these steps:
1. Connect your iPhone to your Mac or PC and launch iTunes.
2. Make sure your iPhone is fully shut down.
3. Boot your iPhone and then immediately press and hold the home button for five seconds or so.
Then on your computer screen it should say,"iTunes has detected an iPhone in recovery mode" and follow the onscreen instructions. And make sure you backed it up recently or you'll lose ALL of your data! Hope I could help and happy repairing.