problem on iPhone 4s after iOS 9 installation

Hi please help. we upgrades the latest ios 9 on our sons iPhone 4s now it is stuck on the plug into iTunes screen. If you push top button and menu button the apple sign comes up then straight on itunes plug in again. We have tried plugging into iTunes where it says it needs to restore this then seems to start on the laptop however after about 3/4 message says can't find iPhone and back to square one. I have tried this several times without luck. Can anyone help? I know last solution is factory settings but want to avoid this if possible as dont want to lose his contacts etc. Thanks