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Are you up to date with iTunes and iOS. Have you tried rebooting your computer. And a hard reset on your phone as well. Hold the power & home button at the same time until you see the logo. Then release the buttons and wait for it to finish. This works on phones up to the 6s/6s Plus. If you have an iPhone 7 then hold the power and volume down button together until you see the logo. Then release the buttons and wait for it to finish. Give my suggestions a try.
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