Deauthorize iTunes
http://support.apple.com/kb/HT6283 doesn't list before reformatting and reinstalling Windows under the Why do I need to deauthorize my computer question? Why does it only list before selling or giving it away, sending it in for service, or making any major upgrades but not before reinstalling Windows? This document was last modified on July 2, 2014.
iPad (4th gen) Wi-Fi, iOS 7.1.1