@MichelDumont
Please confirm that by "50 LMT" you mean that it's a Drive or DriveSmart 50, because there is also a nuvi 50 (LMT only means Lifetime Maps & Traffic). Additionally please confirm that you've removed the microSD card from the device before your attempts to attain preboot.

"System" and "Software Loading"/"Loader" on screen means the device is in preboot mode required to flash firmware as an RGN file. Modern devices are much more difficult to put into preboot and they also hold that state for much shorter time than older models, but once a flash is properly initiated and data transmission commenced they do hold that state until Updater.exe finishes.

G7ToWin only works in preboot/Garmin binary protocol mode. Seeing you have a backup of the file system, look in that for Garmin folder containing "GarminDevice.xml". Open the XML in a web browser or text reader and look for "<PartNumber>006-Bxxxx-00</PartNumber>" near the start of file info. "xxxx" is the four numerals of your device's HWID. Certainly it's 2267 for your device if it's a Drive series "50" however.

I don't have a Drive series device to hand, however if my memory is correct the spot for preboot is over the G or thereabouts. Use your left thumb rather than a finger on the screen with your fingers behind the device as you'll be more likely to find the correct spot for pressure that way and also be able to handle the device more effectively to plug the USB cable into it. Follow this:
  • Plug a 'known-good' USB cable directly into a REAR USB2 port of a Windows desktop PC (don't use a Mac or Linux computer and avoid a laptop/all-in-one if possible), don't use a USB3 port, front port or a hub to connect. Don't connect the device just yet.
  • Have the Cure firmware loaded into Updater.exe with the radio button (dot) next to "USB Device" selected, leave Updater's GUI clearly visible on the desktop screen with the mouse curser positioned over the GUI's "OK" button.
  • Ensure the device is fully OFF, not just in standby. Hold the power button down to force it off if necessary.
  • Hold the device in your left hand applying pressure with your thumb and with your right hand plug in the USB cable to the device's microUSB socket.
  • At that same time watch the window next to "USB Device" and move your right hand quickly to the mouse. When you see the device details appear instantly left-click the mouse (alternatively you can hit the Enter key on the PC's keyboard).
  • Keep firm steady pressure on the device screen until the flash completes indicated by Updater message that it was successful. Usually it's sufficient to hold the screen until after "Loading" or similar message appears on the device screen but continuing to hold is safer.
  • Once you've successfully loaded the Cure fw and restored Mass Storage Mode you can remove any offended files if you know what they are or just clean everything off and load your backup if it's complete and you're sure it's not also corrupted.
  • Finally, load original firmware as an RGN file in Updater.exe following the same procedure as above then connect to GarminExpress to update the device. Don't insert a media card until it prompts you to do so.