my iphone 4 wont update/restore error code 21 keeps coming up

Greetings massianos,

I understand you are unable to restore your iPhone due to an error. That does sound troublesome. The following article provides troubleshooting steps for various errors:

Get help with iOS update and restore errors - Apple Support

Check for hardware issues

Related errors: 1, 3, 11, 12, 13, 14, 16, 20, 21, 23, 26, 27, 28, 29, 34, 35, 36, 37, 40, 1002, 1004, 1011, 1012, 1014, 1667, or 1669.

These errors mean that your device or computer might have a hardware issue that stops the update or restore from completing.

1. Check that your security software and settings aren't blocking your device from communicating with the Apple update server.
2. Then try to restore your iOS device two more times while connected with a cable, computer, and network you know are good.
3. Make sure that your security software and settings are allowing communication between your device and update servers.
4. If you still see the error message when you update or restore, contact Apple support.

Thank you for contributing to Apple Support Communities.

Best,

Bobby_D