Thank caty. I indeed followed the cure and followed your preboot post. But there are two things during the process.

In the updater.exe window, after my unit showing up in the "USB device", it will only stay for like just 10 seconds. During this time, if I press OK to let it flash, it always saying there is no device connected, even I see it recognized. I think there was two times after changing ports and cable, the flashing starts, soon the USB was not recognized quickly and the flashing will stop.

Do you know what was the cause of this? Thanks.

Btw
In the updater.exe window, the error message was indeed "Your garmin device was not responding"