Check to be sure you have guide hairs at all. Then check to see if the "visible" box is checked for the hair group.
I know there is some action that unchecks visible (unintentionally). It has happened to me twice, but I haven't traced the actions yet. I have the latest C6, NOT pro.
The hair seems to work better if there are more guide hairs, rather than less. Also, check the tool settings. Experiment with ridiculously high settings and see how quickly the hair responds. I find that lower settings are waaaaay slow, intended for fine work.
Some guide hair must be selected for the tools to work.