I think Loly is right as usual and there is a problem with the flash chip. It cannot use ldr.bin because it's not booting far enough. One last gasp try before you either strip it for parts or [if you're game] replace the chip which is a very delicate operation involving reballing. You can try to run commands from the card using a patched boot.bin flashed from updater.exe to bypass the rest of the firmware. All credit to kunix, from this post: [Only registered and activated users can see links. ].

Here's a kit with the patched boot.bin and pack for the card:
Spoiler: Patched_boot_kit
[Only registered and activated users can see links. ]

Extract it somewhere convenient then copy the Garmin folder onto a clean card and insert it into your nuvi firstly ensuring it's fully off [hold the on/off button down to force it off]. Open the folder named 'Patched Boot RGN' and drag the file 097201000620.rgn onto updater.exe, select the radio button 'USB Device:' and leave it open and visible on your Desktop. Access preboot as suggested in [Only registered and activated users can see links. ] and click 'OK' on updater.exe immediately the unit details appear in the window to the right of 'USB device:'.
Cross your fingers & go make a coffee or have a beer or ten if it starts to flash because it will take a while.

Good luck.