This article explains how to troubleshoot a USB connection with the following devices and where to get additional information.

iPhone
iPad
iPod touch

When attempting to sync, update, or restore your device, you may see one or more of the following symptoms:

An alert message indicates an unknown error occurred.
The device unexpectedly disconnects during a sync or restore.
Photos downloaded from the device appear garbled or not all photos transfer.
An alert message indicates the USB device cannot operate because it needs more power than is available.
An alert message indicates "this device can perform faster" if you plug the device into a higher speed USB port.

Note: If your device does not appear in iTunes at all, see this article for more information.

Related posts:

1. iPhone, iPad, iPod touch: Troubleshooting contact and calendar syncing via USB on Windows
2. Syncing iPad, iPhone, or iPod touch with iTunes
3. Troubleshooting iPhone and iPod touch contact and calendar syncing via USB on Windows
4. iPhone and iPod: Using the iPad 10W USB Power Adapter
5. iPhone, iPad, iPod touch: Synced photos appear in wrong order