For some reason, I can no longer use the dynamic hair in C6.1 pro since the upgrade.  After I create the hair, none of the tools has any effect on it.  If I activate the brush tool, the hair disappears whenever I have the mouse clicked.  All the other tools just allow me to draw a selection box around the hair, but nothing happens.
Is this happening to anyone else?

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.

Blackcat.
I used Hair just a couple of days ago.C6.1Pro

Today it wont work--at ALL!
Something very wrong has happened.

bwtr

Blackcat.
I am finding other problems also.
Did you just update a DCG patch by any chance?

bwtr

After closing down the computer and restarting it again, 3 times!, everything is working OK for me.

A very strange one.

bwtr

You can look for the 6.1.1 version that is already online too:

http://www.daz3d.com/i.x/support/downloads/-/?product=car_down&_m=d

Follow me at euQfiz Digital

I figured out my initial problem... the default setting for hair now is 0 guide hairs (it used to be something besides 0).  Once I set it to have guide hairs, my problem goes away.
Thanks for everyone's suggestions.