I have the same problem. I can pickpocket him, but I can't talk to Arngeir. I've tried Shouting at him, using the disable/enable/recycleactor commands, hitting him, reloading old saves that I thought weren't corrupted, removing my hood even though I don't have the Sneak Tools mod, etc... Only thing that has worked for me is to kill Arngeir while he's asleep. I think there's a perk -if you have the mod Perkus Maximus- that allows you to kill NPCs while they're sleeping by pressing E, and choosing to kill them. So I kill Arngeir, and use the resurrect command while standing near him, and mash E as soon as I quit the console. Usually, he goes on to finish the quest by summoning the other greybeards and they do their little ritual by Shouting at me. That said, I cannot talk to him after that, so he can't tell me where the Words of Power are located, etc... Maybe if I finish this Redguard quest+Delphine's quest at the Thalmor embassy? I'll edit it if I find something that works, or if there's a quest to finish in order to be able to talk to Arngeir again. Annoying that there are still bugs these days on Skyrim. EDIT: Eureka! So, finishing the quest 'In my time of need', with Saadia, whether you kill Kematu or capture Saadia is enough to debug Arngeir, for some weird reason.
