I am currently having issues with my z-axis. I am unable to perform both a G28Z command and a G0Zxxx command. My steppers (two steppers for z with 8mm acme screws) just buzz briefly then stop.
It sounds like there is not enough current to drive them.
However, I am able to move the axis both up and down using the manual controls inside of a program such as pronterface or repetier.
This is a brand new build and I'm using an autoleveling probe. I'm not sure if any of that would be making this issue.