I shattered the screen on my iPhone4 (verizon) and it was fine for a few weeks. I finally decided to take it to a repair shop and have a new screen put on it about a week ago. Two days ago it randomly turned off by itself and then yesterday it got stuck on the recovery screen. It only powers on when plugged in and only goes to the recovery screen. I tried plugging it into iTunes and Recovering but I just get the error code 21. I've read other threads on this website but they either don't make sense (because they are for jailbroken phones) or just dont work for me. I'm not worried about losing all the data on my phone.. is there any way to fix this? or do I need to just take it back to the cell phone repair shop?

Have you ever run TinyUmbrella? Getting an error 20/21 when you're restoring a stock firmware usually happens when your hosts file has a reference to gs.apple.com and it should not. Check your hosts file -- on Windows this is in c:\windows\system32\drivers\etc\hosts -- make sure that any lines that include gs.apple.com are removed from the file, then try the restore again.

If it still fails, read the restore problems link in my signature and follow the instructions to post a useful restore log for us and we'll go from there, but in all previous cases, this was due to some straggler data left by earlier jailbreak processes, etc.

Hello i have the exact same problem as you - my iphone is stuck in recovery, not jailbroken and came after cracking the screen - i just get error code 21 when i try to restore.. please tell me if you solved your problem and how! thank you