you may have 2 kind of problems:
a- software or hardware problem in your laptop. (iTunes not correctly installed or driver of USB or damaged USB port or using a USB port not directly)
B- software or hardware problem in your iPhone.( locked phone, damaged iOS of your iPhone,...)
then I recommend you check these:
1- iTunes to be the last version. you may need to uninstall it and install again.
2- your iPhone not to be locked when connecting to the computer.
3- the driver of USB port you are using, installed correctly.
4- with a previously back up of your iPhone, you can restore your iPhone to the original iOS. be careful, not to lose your data, by turning off the device and turning on to the recovery mode.
5- restarting the 2 devices at the end of these processes.
This problem started to occur with my iPhone 4S on a clone computer running Windows 7 Professional 64bit after I turned on Genius in the app store. Prior to that, I never had the error.
The problem occurs when I unplug the phone to use it during the day with iTunes always loaded and running. When I am done for the day, I plug my phone in and click Sync. After turning on Genius in the app store, when I go to plug my phone back in, I get the error.
I have found the easiest way to fix it is to unplug the phone, close iTunes, plug the phone back in, then start iTunes back up. Apple messed something up in version 10.7 of iTunes and ios6 to cause this problem.
iOS: Device not recognized in iTunes for Windows
Your iPhone, iPad, or iPod touch may not appear under Devices in iTunes after you connect it to your Windows PC. Any of the following may also occur:
The device cannot be restored in iTunes.
An exclamation point, question mark, plug symbol, or "X" appears next to the device's entry in Device Manager.
During an update or restore, the device may no longer be recognized by iTunes.
Note: If you have an iPod classic, iPod nano, iPod shuffle, or any older model of iPod that is not an iOS device, follow steps in iPod not appearing in iTunes instead of the steps in this article.
Follow these steps, testing to see if the issue is resolved after each section.
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1. Update iTunes
Check that you have the latest version of iTunes installed on your computer. In iTunes, select Check for updates in the Help menu.
2. Check the USB cable
Verify that the 30-pin to USB cable or Lightning Connector to USB cable is free of debris and not damaged. If another cable is available, test with that cable instead.
3. Verify that Apple Mobile Device Support is installed
iOS devices require Apple Mobile Device Support, which should be automatically installed with iTunes. To verify whether it is installed, follow the steps appropriate for your Windows operating system below.
Windows XP: Click Start and choose Control Panel. Open the "Add or Remove Programs" control panel and verify that Apple Mobile Device Support is visible in the list of currently installed programs.
Windows Vista and Windows 7: Click Start and choose Control Panel. Click "Uninstall a program" (or if using Windows Vista's Classic View of the Control Panel, click "Programs and Features"). Verify that Apple Mobile Device Support is visible in the list of currently installed programs.
Windows 8: Move the cursor to the upper right corner, click the magnifying glass, type Control Panel, and press Return. Click "Uninstall a program". Verify that Apple Mobile Device Support is visible in the list of currently installed programs.
If Apple Mobile Device Support is not listed, remove iTunes, QuickTime, Apple Software Update, Apple Application Support, and then reinstall iTunes. Follow the steps appropriate for your Windows operating system below:
Reinstall iTunes for Windows XP
Reinstall iTunes for Windows Vista, Windows 7, or Windows 8
If after reinstalling iTunes Apple Mobile Device Support is still not installed, follow steps in Trouble installing iTunes or QuickTime for Windows.
4. Restart the Apple Mobile Device Service
Follow the steps in How to restart the Apple Mobile Device Service (AMDS) on Windows to restart the Apple Mobile Device Service.
5. Verify that the Apple Mobile Device USB Driver is installed
For Windows XP
For Windows Vista, Windows 7, and Windows 8
If the Apple Mobile Device USB Driver is not listed
If the device is not recognized while in Recovery Mode
6. Check for third-party software conflicts
Certain phone and cellular device connectivity software from vendors such as Samsung, Nokia, Bora, Novatel, Sony, Android, LG, Sierra, Huawei, Pantech, or Motorola may cause your device not to be recognized. If you have such software on your computer:
Uninstall the phone or cellular connectivity software temporarily, and test. Contact the manufacturer of this software for assistance in doing this. If you use the third-party phone or cellular device for your Internet connection, try connecting to an alternate network using Wi-Fi or Ethernet.
Remove iTunes and all related Apple software by following this article (for Windows XP), or this article (for Windows Vista, Windows 7, and Windows 8).
After reinstalling iTunes, test the device.
If you still need your third-party phone or cellular connectivity software that was removed, reinstall this software and test your device to ensure it still functions with iTunes. Contact the vendor of your phone connectivity software if the issue returns.
Also, third-party security software may conflict with iOS devices connecting to iTunes. Follow this article to troubleshoot issues that may be caused by your security software. After resolving any issues you may have with your security software, you may need to try the steps in this article again.
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I am running Windows 8 and using an iphone 4S. I have been troubleshooting this problem all evening. I connected my phone to a win 7 machine and got no errors; it connected to Itunes perfectly. Out of a whim I went down to my car and got an old cable which solved the problem! Hooray!!! The cable I have been using works fine for other devices (IPAD, etc.) but apparently does not work for iphone. Make sure you are using a cable that is known to be good and compatible with your device. I certainly don't understand how these cables can be different but they apparently can be. I hope this helps before you begin de-installing/reinstalling software, USB drivers, etc. Good luck!