My daughter's iphone4s battery died completely and wouldn't charge at all. So I purchased a new battery and changed it out. It will come on now but only shows the apple icon. I've tried to turn it off but it doesn't give the swipe feature to turn it off. I've tried to restart it by holding down both buttons and when it comes back up it's just the apple icon. Then I happened to check to see if sims card was in slot and there is not one. This is her second phone we replaced it about a year ago and I thought we put the sims card from her original phone into this one. Could not having a sims card in phone be the reason all we get is apple icon? If so her sims card has been stolen as she has had no issue with phone before now.
SIM card is not needed on 4S, and has no relationship to the current problem.
I did as you directed and when it finishes extracting files from my iPhone then goes to update it an error pops up. It says iPhone is unable to update error (21). I've updated my Microsoft windows and downloaded current iTunes.12.1 I believe it is. Any further suggestions on what can be wrong and what to do to fix phone?