This tutorial is out of date. It worked for people who had Apple TV 2 with 4.1.1 and accidentally updated to 4.2.1.
Please follow these instructions instead:
My friend accidently updated his Apple TV 2G to version 4.2.1 (2100) iOS 4.3 which removed jailbreak and XBMC I put for him before with version 4.1.1. I wrote this tuorial: http://arturito.net/2011/04/09/apple-tv-2g-untethered-jailbreak-and-xbmc-installation-ios-4-3-with-sn0wbreeze/
which deals with iOS 4.3 and installs XBMC. All installs well but…. we all got audio device error and could not play MKV files.
I turned to Seas0nPass and PwngeTool but it had the same problem. But thanks to users comments especially Fluxx and Czechmarty I managed to fix it. I still don’t know how I managed to restore to previous version without SHSH blobs ………but I did. I assume that if Apple TV firmware version shows 4.2.1 (2100) the iOS must be 4.3. I asked question on XBMC forums in order to confirm that.
http://arturito.net/2011/04/12/apple-tv-2g-untethered-jailbreak-and-xbmc-installation-ios-4-3-working/ All replies I got confirmed that 4.2.1 (2100) for ATV2 is iOS 4.3.1 Well let’s start: Download: 1. iTunes 10.2.1 – might work with newer version but this is waht I tried and worked for me.
http://www.oldapps.com/itunes.php?old_itunes=71 2. Apple TV Fimrware 41.1 (iOS 4.2.1)
3. Uninstall your current version of iTunes and install version 10.2.1 4. Fire iTunes, connect Apple TV with USB cable only. Let Windows install all drivers.
5. Once you see Apple TV in iTunes hold Shift and click Restore. 6. Select AppleTV2,1_4.2.1_8C154_Restore.ipsw and wait until it completes 7. Go to this post http://arturito.net/2011/02/14/apple-tv-2-untethered-jailbreak-on-windows-and-xbmc-media-centre-installation/
and jump to point 1 (Running GreenPois0n)