Troubleshooting USB
Connect the iPhone or iPod touch to a different USB port of the Mac or Windows PC. It is preferable to use the USB 2.0 ports integrated in the computer. If you have connected your iPhone or iPod touch to the USB ports on the front of your computer, try connecting them to the rear USB ports. After this, try to restore the device in iTunes.
If the problem continue:
See "Solving Problems with USB Connections" for additional suggestions related to USB connections, and follow the steps indicated to restore the device again.
If the problem persists and you use a Mac, try to re-establish the USB connection by following the steps described in this document, and then try to restore the device again.