I was facing the same issue after upgrading to Windows 8.1. You need to remove EVERYTHING that has anything to do with iTunes to fix this problem. Make sure to remove Apple mobile device support, bonjour, Apple software update, Apple application support and of course iTunes. This article will help you to remove everything: http://support.apple.com/kb/ht1923
Now re-install the iTunes software and you’re good to go. I hope it helps.