Thank you for the clarification.
Let's first try the easy fix first. Hold down the home button and the power button at the same time for 20 seconds or until it resets. Once it resets, let go of both buttons. If that fixed the problem, you are good to go. If the problem is not fixed, please continue below.
Only follow the instructions below, if the instructions above didn't help.
You will have to restore the iPhone to a base firmware install, which will erase everything on the iPhone, but you can later restore the contents of the iPhone to a backup that you have on the computer (the same computer you used in the past to sync the phone with):
- You will need to have the iTunes application installed first. If you do not have it, you can download it for free from the following site: http://www.apple.com/itunes/download/
- Press and hold the top power button until the iPhone turns off
- Connect the iPhone to the computer that you have been using the phone and iTunes with
- Hold down the HOME button on the front while pressing the Power button (continue holding the home button)
- Continue to hold the HOME button until you see the "Connected to iTunes" message
Option 1: In the Summary tab, click Restore and follow the prompts. (THIS WILL ERASE everything on the iPhone and make it just as it was when you first purchased the phone).
Option 2: Click the button on the top right of the iTunes window for your (iPhone) and then click the Restore button.
- Once that is complete, right click the iPhone listing in the left panel of the iTunes window
- Choose "Restore from Backup"
- Choose a backup date and restore.
Now your iPhone will be back up and have all the restored information from your last sync.