Error 1604: This error is often related to USB timing. Try changing USB ports, uninstalling and reinstalling USB ports, and other available USB troubleshooting steps (troubleshooting USB connections, device not recognized properly, computer won't recognize a FireWire or USB device). If you are using a dock, bypass it and connect directly to the USB 30-pin dock-connector cable. If the issue persists on a known-good computer, the device may need service.
If the issue is not resolved by USB isolation troubleshooting, and another computer is not available, try these steps to resolve the issue:
1. Connect iPhone to iTunes, confirm that the device is in Recovery Mode. If it's not in Recovery Mode, put it into Recovery Mode.
2. Restore and wait for error 1604.
3. When prompted click OK.
4. Close and re-open iTunes while iPhone remains connected.
5. iPhone should now be recognized in Recovery Mode again.
6. Try to restore again.
If the steps above do not resolve the issue, try restoring using a known-good USB cable, computer, and network connection.