Like many others on the forums I got stuck with this issue today. Tried the suggested self-help methods:
1. soft reset by holding Light button 30sec -> boot loop continues, clock occasionally flashing and returning to loader screen
2. hard reset by shutting down, holding Start+Back after restart until hearing sound, releasing Start, waiting for next sound, releasing Back -> boot loop continues, clock occasionally flashing and returning to loader screen
3. doing #2 steps while connected to computer, trying to leverage Garmin Express: shut down clock starts up when connected to usb and proceeds to boot loop, even when doing the Start+Back+bleep sounds process
Weird thing is that unless I remember wrong I had disabled automatic updates due to some version having issues earlier this year. This did not prevent the device bricking itself.
EDIT (fix) - PC USB:
I was finally able to boot the watch by combining tips from multiple guides. Problem was that PC and Garmin Express could not see the watch while it was in boot loop.
Steps which worked for me:
1. connect with USB cable to PC
2. activate Garmin Express "Add a Device" so it starts looking for watches
3. hold Light to shutdown watch while connected, it might reboot itself automatically as its connected but no matter, next
4. hold Start button while watch starts - The Important Bit: hold Start until PC window pop ups note that device has been found, getting sound cues also
5. now you should see the watch storage in Windows Explorer
6. browse to /Garmin/RemoteSW folder in watch
7. delete file: GBE.bin
8. you can disconnect watch and see if it boots, after this the boot went through for me and I could connect back in phone app and start syncing
optional: if you did hard resets etc. you might want to restore backup in Garmin Express from "Tools" menu, I had no compatible backups stored unfortunately but might have some elsewhere.
