Note: This solution specifically works on iPhone 4S 16GB variants.
iTunes cannot detect the iPhone when plugged in through a USB cable.
If you want to try this solution, be sure to follow the instructions carefully and precisely as elaborated in this page to avoid any possible error to transpire afterwards. We will not be held liable for any other issue or problem that may arise during or after doing this tutorial as we understood you try this at your own risk.
1. Disconnect your iPhone from the computer and reinstall iTunes. Once installation is done, plug the cable back in. Also make sure that you are using the latest iTunes version, preferably 10.6 or higher. You may download it from Apple’s official site: apple.com/itunes/
2. If after the installation and iTunes still could not detect your iPhone, check the Device Manager of your computer and see if there’s any problematic driver. An indication of a problematic driver is a yellow exclamation or question mark on it. Here’s how you do it:
a. On your computer, click the Start button, then right click on My Computer.
b. Select and click Manage. You will then be prompted with the Computer Management Window, which contains System Tools and its sub-directories.
c. Locate and click Device Manager from the list of sub-directories under System Tools. Another window will show up.
d. Locate Human Interface Devices and search for any item which has a yellow exclamation mark or question mark notification on it. This means that this device is problematic.
e. Right-click on the problematic device and click Uninstall.
f. A message box asking to you to Confirm Device Removal will then appear. Click OK to confirm removal of the device and proceed to the next step.
3. Unplug the USB cable attached to your iPhone 4S from the computer.
4. Make sure you have properly installed the latest version of iTunes and then restart your computer.
5. Wait until the computer completely reboots and then reconnect the USB cable from your iPhone 4S to the computer.
6. Open iTunes and your iPhone device will be detected again.