I have few problem after i upgrade windows 8.1 to windows 10 to sync my IPad using iTunes these are few step that will fix your issue:
- Reboot both your iPhone and the PC
- Try a different USB port on your computer
- Install / Reinstall latest version of iTunes
- Install all Windows updates
- Trust your computer prompt
- Check to see if Apple Mobile Device Support is installed from Control Panel > Uninstall a program. If it is not installed, you need to reinstall iTunes.
- Restart Apple Mobile Device Service: Type services.msc in Run (WinKey+R) and hit enter. Locate Apple Mobile Device or Apple Mobile Device Service and then right click > Properties. Then click on Stop to stop the service. Click Start to run the service again. Reboot your computer.
hope this helps