I have just bought an iPod Touch second hand. I tried to update it's firmware to the latest version using iTunes. The update failed and now I cannot access the iPod either directly or in iTunes. Turning the iPod ON the screen shows a 'connect to iTunes' looking icon and does nothing else. Connecting the USB does nothing and the iPod does not show up in the iTunes side bar. The iPod turns itself OFF after a minute or two. What now?
You'll have to connect your iPod in recovery mode. Make sure the iPod is disconnected and turned OFF, so not on stand by, but completely off.
Then, while pressing and holding the Home button, reconnect the USB cable to the device. The device should turn on with the "Connect to iTunes" screen. When this screen appears you can release the Home button; your iPod should now be in recovery mode.
If not already open, open iTunes. iTunes should then display a warning that it has detected an iPod in recovery mode and will ask you to restore it.
Finally got it working - it was the cable! Borrowed a cable from a friend, did the DFM steps as outlined above and it worked (3 attempts, but got there in the end).