I've tried connecting to two different devices with no luck. Software is up to date (9.75). End result is Garmin Express isn't detecting the unit.
Make sure you are not using a charge only cable, which does not have the data pins connected. It needs to be a data cable.
I was having a similar problem until I cleaned the connector on my 830. Use Isopropyl alcohol to clean the connector on your garmin and try to connect again.