I have a Garmin Zumo 390LM GPS that doesn't show the internal memory or the SD card in windows.
The following tests have already been performed:
a) USB cable is original and in perfect condition
b) Garmin USB drivers are in the latest version
c) Garmin express is in the latest version
d) Windows 8.1 has all updates installed
e) Using the same cable and the same PC you can access other Garmin GPS without any problem
f) I have already loaded a "cure" software and after loading the GPS it was recognized by Windows and new updates of the lifetime maps were made.
g) After returning the firmware from the last original version (see 4.2) and the GPS started not showing the internal memory units and also the SD card.
h) I conclude that I have a software problem that does not show the internal memory and SD in windows, because after applying items (f) and (g) I conclude that the hardware is perfect.
i) I don't have backup of the original files

Has anyone managed to solve a similar problem?