DirectX 11.0
no background app other than win8 standards.
My dragons no longer burn or give up souls.
This started at about lvl 16 (I think about the time I added the Dragonborn DLC and I have since also added Dawnguard DLC and the texture pac)
I am at lvl 20 now and the last five dragons killed have not burned. Not the same dragon, not the same place.
I removed the game, deleted the install directory and re-installed it. No mods and still dragons don't burn. Now what?

Since your on PC, have you tried the Unoffical Patches for the game and the ones for the DLC's?