Ok, so I sided Dawnguard. During the main quest I became a vampire lord to enter the soul cairn. I cured myself soon after. After the main quest I decided to become a vampire lord again. Serana infected me and I got the power. Whenever I use the power it doesn't do anything and then the power grays out (like after you use your daily stone power.) Nothing happens and I remain in human form. Any ideas?

Maybe related to the Atronach and Lord Stone bugs, with those two (Aetherium Crown) I can't summon Deadra or Dragons. Until I download the fix that someone has put up on Nexus.
Something to do with high resistance and magic absorbtion.

Well, i am using the Aetherium crown. I'll grab the fix from the nexus and see if that works. Thanks for a response.

Unfortunately that did not work.

Fixed it by typing " set dlc1vampirelorddisallow to 0 " in the console