Board Thread:Skyrim/@comment-108.243.120.98-20131102233926/@comment-6881629-20150215164739

The bug is caused by attacking Alduin before Parthanaax tells you to so the most reliable fix is to reload to before reading the Elder Scroll or if you have no save try fast traveling to and entering High Hrothgar. Seeing as your on PC you could open the console click on Alduin and use the commands disable and then enable to reset him.