First, what system specs do you have?
Second, verify your core voltage with gpu-z or something. It's probably somewhere around 0.95v...It shouldn't be at 0v. The voltage feature is probably locked for your card, like it is for mine.
^^I also cannot unlock the voltage for my card. Does anyone have suggestions? I checked the boxes under settings to unlock the voltage modifier, and I am running afterburner 2.1.0 which supports unlocking the vcore on the GTX570.
8 gig ram