Keep trying to flash over and over. Bootlooping devices can be tricky to flash and perseverance is key. By the way, telling us all the circumstances how it became bricked using GarminExpress is not just important it's crucial which is why i suggested in Post #2 you read this: [Only registered and activated users can see links. ] and then report.

If you're still unable to flash any firmware in preboot after numerous repeated attempts then it could be that the flash chip is damaged, sorry. If the problem is indeed hardware damage then there is no software solution.

There is also a way to attempt the flash using a modified boot.bin as an RGN to execute text commands from a microSD card so don't give up but keep trying to get the Updater.exe flash to complete before we try that. I once got an Updater.exe flash to complete on an old StreetPilot after trying 10 times every morning for over a week. Persistence pays off sometimes with stubbornly bricked devices.

EDIT: I guess you mean "created the RGN" not GCD in above post.