The xml is your configuration file, it will have the name of the profile you are using and will be in the main Mach3 folder, so it may be something like DynaCNC.xml or may just be Mach3Mill.xml

Can you load the standard Mach screenset and test with it, you may get error messages showing at the lower left which may hold a clue.

Are there any external buttons on your control panel?
Hood

Was there ever a resolution to this thread? I am having a similar problem

https://www.youtube.com/watch?v=h6sFaveKYUI

Ron,
I have replied in another thread, but what Lookahead value are you using?
John Champlain