When you try homing and the system goes into "disabled", what message(s) do you see in the Mach4 status line (lower left of the wx4 screen set). Or click on the "history" button to see all of the messages, not just the most recent one. You can also turn on Mach4 logging (Diagnostics menu, then "logging") to see even more information. The PMDX plugin usually displays some kind of message if it has to disable Mach4. Post the contents of the "history" and "logging" windows here.
There could be noise coupling into your limit switch inputs, or maybe even the EStop circuit. How do you have them wired? Do the limit switch wires run near any high current power wires - including a VFD? spindle motor? Plasma torch???????
Can you drop down to a single motor and home/limit switch, and disconnect everything else? If you have an EStop switch, replace it with a short jumper wire (or the PMDX-424's original shorting clip). Then try homing that one motor/axis. Do you still see this problem?