When manually controlling the z-axis in reprap, it works fine. If I use the home button, it doesn't move. Instead, it stalls/freezes/hangs. It attempts to turn, but can't successfully make a full turn.
If you run M503 you should be able to see your max speeds. They, along with your homing speeds, are probably far too high and causing skipped steps (no movement). You can lower them down temporarily with M203. http://marlinfw.org/docs/gcode/M203.html