Unable to deal damage to Alduin

I'm trying to beat Alduin, at the Throat of the World. But I can't hurt him!

I'm level 47 and I'm wearing all Ebony armor, the helmet is +35% for archery. The weapons I've used are Dragonbane and a Daedric bow w/ shock damage. Everything is legendary. Is this some kind of glitch?

Solution 1:

The Elder Scrolls Wiki reports a bug similar to the problems you are experiencing.

Taken from The Elder Scrolls Wiki: Skyrim: Alduin's Bane: Bugs:

Alduin may become invincible during the fight. According to the patch notes, this bug was supposed to have been fixed by version 1.9.26.0.8 of the Skyrim Official Patch. However, there have still been confirmed reports of this bug occurring; specifically, if you exit dialogue with Alduin prematurely after returning from the vision in the Time Wound, or if you die during the fight with Alduin and reload the game. Open the console, click on Alduin, then use the command disable followed by enable. This may result in Alduin being able to be damaged normally. Saving immediately before combat starts, then fast-traveling away and returning, may fix this. As of 1.9.32.0, the game creates an autosave after exiting the Merethic-era cutscene, right before the conversation with Alduin.