I tried to update my iPhone 4s to iOS 9.1, but the ISP's firewalls at my internet access point interfered with the installation. I tried plugging the iPhone into a computer outside of the firewalls. Windows detects the iPhone as a USB drive, and iTunes doesn't recognize it at all.
The phone itself seems to have no OS installed whatsoever, and all it can do is give me the Apple logo or tell me if the phone is plugged into a computer or not (the phone does show an iTunes logo, oddly enough).
What can I do to make iTunes recognize the phone or to make the iPhone initiate a reset / iOS update?