To synchronise the data on your computer with your iPhone, iTunes must recognise the device. The iTunes application is not only used to sync data but also to update the software on the iPhone when updates are available. There are several reasons why your iPhone may not be recognised by iTunes. The problem can originate from your computer, from iTunes, or from the iPhone. Apple has provided a troubleshooter that can help to identify and resolve the problem.
Launch a Web browser; go to the "iPhone Not Appearing in iTunes" troubleshooting assistant webpage.
Click "Begin," and follow the troubleshooter instructions. Check your system to be sure it meets the requirements needed to use your iPhone with iTunes. For example, the latest version of iTunes must be installed, and a USB 2.0 port must be available to connect your iPhone to the computer. Upgrade the software or hardware on your computer if necessary.
Charge your iPhone. If the iPhone is low on power, it will not appear in iTunes. If a low battery is the problem, your iPhone will appear in iTunes approximately 10 minutes after charging via your computer's USB port.
Connect your iPhone directly to a built-in USB port on the computer. If you connect the iPhone to a port that is on an external peripheral such as a keyboard, the iPhone may not appear in iTunes.
Restart your iPhone. Press and hold the "Sleep/Wake" button; slide your finger across the screen when the slider for turning off the phone appears. To turn the iPhone back on, press and hold the "Home" and "Sleep/Wake" buttons simultaneously until the Apple logo appears. Reconnect the iPhone to your computer to see if the problem is resolved.
Restart your computer. Sometimes restarting the computer can by itself resolve any conflicts that may prevent iTunes from recognising your iPhone. Launch iTunes, and reconnect your iPhone to the computer. Check to see if the problem is fixed.