i tried to update my ipod but then it didnt work saying that an unknow error has occured, now itunes is not recognising that an ipod has been plugged in and the picture that comes up when you first get it is on my screen, i dont know what to do?

What was the complete wording of the error message? Usually an error number or more information is contained in the eror message.

Put your iPod Touch in DFU mode, restore and update it with iTunes.

Here's how:

• Connect the iPhone to your computer and launch iTunes
• Turn the iPhone off (hold down the power button at the top of the iPhone)
• Hold down the sleep/power button and home button together for exactly 10 seconds, then release the power button
• Continue to hold down the Home button until a message appears in iTunes telling you an iPhone in recover mode has been detected

• When you are in DFU mode your iPhone screen will be completely black

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.

Error 1600, 1601, 1602

Follow the steps listed above for Error 1604. This error may also be resolved by disabling, deactivating, or uninstalling third-party security, antivirus, and firewall software. See steps in this article for details on troubleshooting security software.