Mass Storage Detection Garmin | Why doesn't my computer detect my device when it's in USB Mass Storage Mode?
From Garmin Support.
All current Garmin devices, when connected to a computer, will communicate in either Mass Storage or Media Transfer Protocol (MTP) mode. If the computer is not detecting the Garmin device, there are a few troubleshooting steps that can be done.
1.Unplug the USB cable from the computer.
2.Turn the device off and then back on again.
3.Plug the USB cable directly into the device and the other end directly into a USB port on the computer and not a hub or docking station.
The device should automatically go into Mass Storage or MTP mode, which is indicated by a picture of a GPS device connected to a tower on the Garmin screen.
To check the computer's recognition of the device on a Windows PC click on the Start menu and select (My)Computer. The device will show in this window if the computer recognizes it. On a Mac, the device will show as an icon on the desktop, labeled "GARMIN", or it can be found by selecting Finder from the dock and viewing the device list on the left-hand side menu within the window.
Note: If the computer still does not detect the device, try plugging it into a different USB port. If the problem persists, try another computer, if available. Ensure the USB cable is not connected to a cradle, if one is attached to the GPS.
Ensure the cable is a compatible USB cable.
One problem and solution reported by POI Factory member JD4x4 was that some newer Garmins seem to require a bit more power on the USB port than other models.It may show the PC connection screen, but will fail to be recognized by the PC (especially a newer tablet and/or laptop).JD4x4's solution was to purchase a USB hub that supplies it's own +5v power.
If you still experience problems, contact Product Support.