Don' know if this is a glitch or I'm an idiot . . .

Going thru Sovngarde. I killed a dragon preist, who had the diamond claw-key on him for the key-puzzle door in the same room. How convenient. Simple -- look at the key, match the symbols, insert key, move on, right?

I can't activate the rings. No matter how close I get, they won't activate. The "(A) to activate outer/middle/inner ring" prompt appears, but when I press "A" nothing happens. I've had no problems with any of the other ring doors.

Please someone tell me there's some sort of switch I'm being an idiot for not seeing. Please?

I had that same thing happen to me on the golden claw door. Just leave the area and re enter and you should be able to turn the rings.