I had the exact same problem. Only I would have power to Z (could not spin screw) then as soon as i tried to move Z, mach would show it moving but the motor would lose power instantly (could then move screw after pushing pgup/pgdn) I have replaced the driver on the controller to see if that works but have not tested yet. I will not be able to test a couple days because i am leaving town but i will let you know as soon as i return and test it out. I have a HobbyCNC Pro board. After reading yours it sounds as though we may be having the exact same issues.
Here is a thread that i started for this issue as well. See if what they had to say could help you.

http://www.machsupport.com/forum/index.php/topic,24465.0.html

TY very much

Have you tried as I said in post 18?
Hood

My similar problem was corrected after I replaced the driver chip. I would recommend trying this also!

I put x on z of the controller and x jogs but z will not no matter where I hook it

But what X and Z, are you just swapping the motor wiring or are you swapping the wiring to the drives themselves?
Hood