All three motors are the same size. Their settings are very close when you look at the graph and it does run smoothly after the initial nudge to get it going.
cdntoolmaker

When you try to move the Z do you hear its making a squealing kind of noise?
Can you swap a drive from the X and try it on the Z and vice versa?
Hood

If its been running that long, and you've changed nothing, looks like either electronic/electrical  or possibly the Z ways and mechanism might need cleaned / lubed even though it operates smoothly by hand.
I dont understand it changing direction though.
And like Hood said, missing steps/ stalling would make a bit more racket than just a humm..unless maybe you were super micro stepping.
Not too difficult to switch wiring just to check, mark the wires carefully and take notes.
Good luck,
RC

Hi guys,
O.k , I'll try your suggestions and take notes. Hopefully a little luck will be on my side. I'll let you know what happens, good or bad.
Thanks for all the help so far.
cdntoolmaker

If you push it and it starts moving then, it sounds like only one phase of the stepper is working. Either a bad connection of the motor wired to the drive or a bad drive. Also, maybe a bad connection on the drive board itself.

Daniel