I acquired a 3 axix custom build cnc router. The previous owner run it with mach3 and he game me the config file. Before I spend the $$ I want to make sure it will run. I cant manage to load the xml, I put it in the same folder where mach3.exe is and when I open mach 3 i see the xml config but when I click on it it just shows a blank window. The xml file is not empty, so I was wondering if i can't load it in demo mode.

You can load any .xml file in the demo version.
Does the .xml reference a custom screenset that you don't have?

To load Mach3 with a specific xml file, change the target on the desktop shortcut to:

C:\Mach3\Mach3.exe /p xmlfilename

Do not include the extension in the xml filename, and make sure the xml filename does not have spaces in it, or it won't load.