1) Have you selected Garmin Monterra on the GPS Set Up screen?
2) If you open Windows Explorer, does your Monterra appear as a removable drive with a drive letter (e.g. F: or G: or K:)? If it appears but there is no drive letter assigned your Monterra is probably in MTP mode. For GSAK to connect to the unit, the GPS needs to be in USB Mass Storage Mode (aka Garmin Spanner or Garmin Serial). I don't have a Monterra so I don't know how you switch the interface mode, but if you can't find it in the manual, Garmin support should be able to tell you.
2) If you open Windows Explorer, does your Monterra appear as a removable drive with a drive letter (e.g. F: or G: or K:)? If it appears but there is no drive letter assigned your Monterra is probably in MTP mode. For GSAK to connect to the unit, the GPS needs to be in USB Mass Storage Mode (aka Garmin Spanner or Garmin Serial). I don't have a Monterra so I don't know how you switch the interface mode, but if you can't find it in the manual, Garmin support should be able to tell you.
