error 1604, cannot restore iPad

Check out this Apple article -> iTunes: Specific update-and-restore error messages and advanced troubleshooting

Error 1604

This error is often related to USB timing. Try changing USB ports, using a different dock connector to USB cable, and other available USB troubleshooting steps (troubleshooting USB connections. If you are using a dock, bypass it and connect directly to the white Apple USB 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 the device 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 the error.
3. When prompted, click OK.
4. Close and reopen iTunes while the device remains connected.
5. The device 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.

Are you able to restore the iPad from Recovery Mode or from another computer?