The problem is this- Alduin takes no damage. At all. Nothing I do harms him. Twenty minutes of fighting, never harmed him at all. I'm right next to him, bashing away, but no damage. I didn't have any issues the first time. Any ideas as to WTF?

IIRC, You can get that glitch if you attack or cast dragonrend at him before he finishes his speech.

You should try to reload a save but other than that it has to be one of those glitches that are hard to catch because they dont happen very often.

OK will do. Thanks

Yeah that part's pretty glitchy.
No need to fix that one either, Beth! No rush!