I have a Maker Farm Prusa i3v 8" i just finished building. Initially when i first homed it, it ran fine, it even ran a test g code for movement. The problem is now the Z axis wont move anymore. First i checked for physical issues such as binding or nuts coming out of traps, everything's OK there. In Pronterface i can move x & y no problem, but Z will not move, there is no noise from the steppers. Also unusual is the the Z axis is not on the endstop, its resting on its own in a spot (the hotend is about 2mm off the bed). I ordered some new end stop switches to try on my Z axis....any thoughts? I'll update after switch install.
If you are using Repetier the code to test the endstops is m119 I think. If your z stop is triggered, you may have to invert it in the config.h file. I had this same issue for days before i figured out the control board was reading the switch as normal close instead of normal open. Hope that helps!
Try sending a motion command manually, such as G1 X20 Z10, to eliminate any bugginess from the software interface as a reason for the Z not moving properly when commanded to. Next you could check the park location in Pronterface, perhaps the extruder head is sitting there waiting for the next command.