Assuming that you are running on the same computer as before, your PMDX plugin should be there, but the Mach4Mill profile does not have it enabled. You can try again by copying the PMDX-Sample profile instead of the Mach4Mill profile, or you can manually enable it by going to >Config >Control and select the Plugins tab. If the PMDX plugin is on your computer you will see it in the list under this tab. Make sure it has a green check in the Enabled column of the chart. Then hit the Apply button in the lower right corner of the window. You will need to shut down and re-start Mach4 so that Mach4 includes the newly Enabled plugin among those you can select.