I'm on the quest Alduins bane and i'm attacking him but his life bar is still full lol.
should i uninstall dawn guard or something because i beat that before i did the main quest line
or is it a patch gone wrong ?
Any ideas?

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It's a bug caused by attacking him before he's done talking. It happened to me as well, but I reloaded and waited for him to be done saying his lines before attacking, and the problem stopped.

i tried that it didnt work for me so i un installed dawn guard it worked fine until it auto saves then game crashes