Brad,
It might be worth taking a look at the axis drive amplifiers when you have the machine powered on. See if you have some LED's on, or not as an indication that power is getting to the amplifiers.
History: I used to have the odd spurious fault where I would see an Z axis drive fault alarm, unless I was using the A axis, in which case the fault was the A axis drive fault. It turned out that I had a weak and failing power supply to the drives. Not the main power, but a small standalone one that feeds 12v in there someplace (on a '96 VF3). Anyways, the alarm codes did not really mean what they said, it was simply a case that that power supply had failed, and the Haas interprets the dead amp fault as an amp fault, not as a failure of this little power supply.
If it is that one, I was able to source an inexpensive exact replacement through Newark electronics.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)