I have acquired a Garmin Dezl 580LMT-D sat nav.

I plugged the unit into a real Garmin automotive charger. After a few minutes the unit automatically booted up (flat battery?) and appeared to work 100%. I was able to log on to my wi-fi connection and a maps/software update would have taken over 3 hours so I decided to do it later.

With the sat nav appearing to work 100%, I powered down BUT the unit would not boot up on pressing the on/off button. I held in the on/off button to do a soft reset and the unit booted up and was again working OK..until I powered down again. I had to keep holding in the on/off key or leaving the unit on charge and it eventually booted.

I decide to follow the various You Tube reset guides and do a full reset...and also erased all user data. The unit again worked BUT would still not boot up using the on/off key.

I attempted another full reset BUT now the unit only powers up at some random time after connecting the Garmin charger and then freezes on the "Warning Allow" screen. When I hold in the on/off key I get the "Turn Off Device / Cancel / Off" message BUT when I press Off the screen remains frozen and nothing happens. The unit is also NOT recognised when I try to connect to a pc running Garmin Express.

I have opened up the unit and disconnected the battery for 30 minutes BUT when the battery is reconnected the unit still does not boot up when the on/off key is pressed. When a charger is connected the unit will again boot after some time but again freezes on the "Warning Allow" screen.

Any ideas? I was thinking that the boot software / firmware is corrupted? Maybe the corruption was only "minor" to begin with (so the unit worked but would not boot up after powering down) but the corruption has got worse after doing multiple resets so the unit now freezes on the "Warning Allow" screen . Maybe I need to reinstall the boot software/firmware using an SD card is this is possible?

Thanks