Thank you very much for your help and time!

I know the procedure to enter the preboot mode, I did it on many other devices without problems. On this device I didn't manage the preboot mode even before making any changes. From what I found on the internet, the DS 50 enters the preboot mode by pressing with the finger above and between G and A in the GARMIN logo, but I never succeeded.

I also know how to use the Updater, I have used it many times to unlock Garmin devices.

I reformatted the device with RMPrepUSB, with the settings indicated by you and I created a Garmin folder in the device, I disconnected it from the computer and restarted it, but the result is the same. Starts, the GARMIN logo appears, then the computer image appears and goes out. That's all!

In connection with the belief that the device now has the firmware dezl 2826 is due to the fact that I used only this dezl firmware and that in RMPrepUSB on DRIVE appears Garmin dezl System, even if I formatted the device with this program or with Windows.