Thread: 3790 -> 3490 all file system missing

Problem definition:
One of my friends asked for help about following - he has 3790 -> 3490. Explained me that he did not use the unit for month or so. When he started it up - nothing happened. Of course he charged the unit, conected it to computer and found that all files missing. So far, so good. I tell him to create a Garmin folder,
to restart the unit, to check for GarminDevice.xml file presence and to connect to WebUpdater, i.e. normal procedure.
The long way to nowhere:
The unit has created GarminDevice.xml.
In the beggining WebUpdater detected the unit, start update process, but when downloaded FW it says "No unit attached" or something like that end that was the case.
OK I said then something wrong with cable or with drivers. Cable was changed, USB drivers reinstaled. Even computer has been changed...
WebUpdater still can not update the unit.
Next step was to try to load FW through Updater.exe. After loading USB drivers again succesfully loaded FW, but that not helped much with other files and WebUpdater.
Formated the unit as described in the thread How properly to format ..... Again same story. After restart the unit creates simple file structure and GarminDevice file, but the problem still persist.
The problem is that non of Garmin programs /WebUpdater, Garmin Express etc./ can not detect the unit. Updater.exe - yes, but that not help much.
Sent to my frien a copy of my unit file system. Wiped unit, copy/paste all file system without GaminDevice.xml and no result.
I have even uninstalled all Garmin programs from my friend computer in order avoid any doubts of unproper drivers behaviour. Nothing changed again.
Even windows says on first connection after all Garmin programs uninstall that the drivers can not be instaled succesfully.
The request:
I'll be much obliged to any advice.
Most probably I'm missing something and I'm opened for any sugestions.
The bad thing is that I have no the unit in my hands and some of the procedures I'm doing with TeamViewer on the remote computer, but that is life...