You clearly have some type of hardware failure. This process is way to simple to not be able to accomplish it without that issue.
ok here: Pre: Go to /Applications/Utilities/Activity Monitor a: open it b: search for iTunes Helper c: quit it 1. open pwnage tool 2. click dfu 3. plug in ONLY the usb 4. follow steps 5. Restore with custom firmware in iTunes My tv 2g was doing the same thing that was happening to yours and I got mine jailbroken with these steps.
It's your cable. It's faulty. I just replaced mine and I got the *beep-boop* from new hardware and it's detected in iTunes.
Just a thought, but many micro USB cables are made to only charge devices, if you are using one of these you will get power from the Apple TV but it will not show up in iTunes due to lacking the data wires in the cable. I had the same problem when I was trying to use the micro USB cable that came with my Bluetooth headset.
Still have problem on jailbreak your Apple TV? Read these tips: http://www.appletvhacks.net/2011/02/16/how-to-jailbreak-apple-tv-2-with-greenpois0n-rc6/ http://atvwiki.dyndns.org/wiki/AppleTV_2