I have tried several days to get into the pre-boot-mode. (205W Board S3, HWID 1091, S/W 6.10)
Laptop can find a new USB device, but cannot find the driver. So I manually install the latest USBDriver 2.3 from website. Then Windows says "An error occurred when installing hardware." And the Garmin USB device icon disappeared... I change a computer, the same happens.

Very interesting, if I press "Battery" icon to get into diagnose mode, the GPS connected well with computer. g7towin can get GPS ID and other info properly.
So it means the driver and connection between GPS and laptop is OK. But just cannot work under pre-boot-mode.

I guess it's due to the new HWID or new 6.10 S/W, maybe Garmin change the strategy. I will keep trying and post updates...