Okay, I've had another go. I created a folder and followed the instructions to the point where I start in pre-boot mode. I get the model number in Updater, press Okay. At this stage I get a message saying
"Garmin device is not responding":
1. Make sure Garmin Device interface option set to GARMIN or host mode
2. cable connected
3. turned on
The unit has power, because at this stage Garmin Express opens.
How am I doing?
GeoffRBG.