avirostick,
1. In config>config plugins you need to have the xbox enabled and then click on config and configure it.
    You can't have joystick or shuttle pro enabled also. 
     If C:\Mach3 is your installed directory for Mach, then go to C:\MACH3\PLUGINS and move 
     Joystiick.dll   &    ShuttlePro.dll  to a safe place or as i have done, created a sub-directory under plugins 
     and placed the files there. Now they will not appear in the config plugins pull down.
     You should have a file called    XBoxController.dll   in the plugins directory. 
2. Have you or is Mach configured? 
    check config>ports & pins>input signals  and check and see if the EStop is enabled. You can assign an
     unused port pin # and click emulated.
3. Make sure all the other configs are also configured properly.
Do you have steppers or servos? 
Have you read the manuals? The new "Mach3 CNC Controller Software Installation and Configuration"
which can be downloaded convers a lot of topics on what to do.
Forgot to mention, welcome to the CNC journey.  

RICH