After each step, try to back up your iPhone, iPad, or iPod touch again.
Restart your computer and your iOS device.
After restarting, try to make the backup again.
Unplug your other USB devices.
Unplug everything from your computer except your iOS device, keyboard, and mouse. Make sure you plug your iOS device directly into your computer.
Check your Windows security settings.
If iTunes for Windows stops responding or your backup never finishes, you might need to update, configure, disable, or uninstall your security software. Learn more if iTunes for Windows isn't responding.
Reset the Lockdown folder.
Try resetting the Lockdown folder to start or save a backup.
Try your secondary computer.
If you own more than one, try making a backup on your other Mac or PC.
Free up space.
If iTunes can't make a backup of your device because there’s not enough free space, try freeing some space on your Mac or PC. Then follow steps to make a backup again.