Quote Originally Posted by LAMedia View Post
..... Now, if I insert an SD card, nothing happens, but the SD card appears in Windows, RMPrepUSB or Total Commander.
Have you re-formatted it with the correct settings? If not, please do so and then don't add any files or connect to GarminExpress or WebUpdater. Only this: Make an empty folder named Garmin in the root, disconnect it from PC and power it on by battery then report how it behaves.

I say again, if you cannot access preboot nor get it to flash from card it's not recoverable.