I have a LG G-watch (android smart watch, the square one). I’m not using it much and it mostly seats on my desk, uncharged.
For some reason, I decided to give it another try and it could never start: just after boot, it would say that settings crashed, proposing to wait or to close. Tried all several times and it was stuck in a crash-loop. Rebooting, letting it run out of battery again did not help.
The goal of this post is to keep some notes of the reparation.

Some notes:

• G-watch hardware is called dory and builds are named platina. This helps recognize if the build is for the correct platform or not.
• To go into boot-loader mode, you need to swipe in diagonal when LG logo pops-up (from top left to down right)
• From bootloader, you can do a factory reset. It did not help for me (suspecting issue with hardware or corrupted firmware)
• adb can be found in the recent android sdk, you need to install the usb driver on windows. it handles communication with the device over usb.
• Watch is recognized by computer (using adb devices -l) only when it’s in sideload mode. adb logcat never provided anything, which is not really surprising on a production device.
• Finding a firmware can be fun. I finally had some luck on this website and ended up getting that firmware. Not much chances of failing as firmware are signed : if it’s not for the correct device, it will likely fail with code 7 (had some of these). Likely legit as it comes from googleapis.com domain. I usually am weary of getting stuff from unknown source for firmwares as it can be quite easy to push a virus.
• The physical button on bottom of watch needs to be pressed for ~6s for the watch to shut down. It requires a lot of pressure to press it and hold it (but does a nice click to let you know)

After quite a bit of messing around, it finally reworks. Somehow, one OTA update must have failed.