Had this problem before, never really rectified it.. only way I have found to fix it is by reinstalling and resetting everything. It's a pain and I would rather get the source of the issue. I included a screen shot below to give an example. I noticed it first by looking at the geometry in the upper right hand corner, the toolpath screen. It appeared to only display partial or even just a fragment of the actual program. Running it confirmed that, having stopped precisely where that toolpath stops. There's more gcode below but for some reason mach3 goes all buggy and doesn't go any further or show any hope of going further. Also, this happens with multiple files, every one the same, I've tried at least 10 to no avail. Any suggestions? Am I doing something wrong? Maybe the download I have is corrupted? But i have used fresh copies in the past,it just happens randomly one day when I open it up. Thanks!