It likely will work if my theory stated in Post #2 is correct. If the device is 'bricked' by incompletely loaded/erased firmware then re-flashing via the RGN file in preboot with Updater.exe should restore your 855 to working order. I cannot guarantee that of course and so anything you do must be at your own risk entirely. As shown by the lack of other members posting here, most 'normal' Garmin users such as myself know very little about the inner workings of these Linux-based devices of which Garmin produced very few models several years back. Usually a device running standard proprietary Garmin firmware (which Garmin calls 'system software') having an incomplete or erased fw region will display a start-up message "System Software Missing". In such a case these steps do fix that problem. In your case , I simply don't know sorry.