A lot of iPhone users have complained about issues after downloading the latest software iOS 9.3. iOS 9.3 had caused issues for users of the iPhone 5S and iPad Air and earlier models of both the devices. Users who could not remember their Apple ID and password to login and complete the upgrade found that their devices hung in an inactive state. They had to reset or recover their passwords before proceeding.
Apple has temporarily pulled back the upgrade. An updated version of iOS 9.3 will be released soon, that would have addressed the issue for users of older models.