I've downloaded Garmin Express and installed it, and synced my 405 on June 21. My software is up to date, and my 405 is set on "pairing on". But, i have since recorded 146 activities, however none of them will upload to Modern, and now the old version doesn't recognize my 405???
You should only need to enable pairing mode when you add your device to Garmin Express the first time (or if you ever remove the device from Garmin Express and attempt to re-add it). It might also be a good idea to verify that you've got the latest version of Garmin Express. Instructions for doing that can be found here.
You might also want to try following the instructions here for completely removing the cruft behind from the ANT Agent. Apparently files from the old installation can cause problems for Garmin Express.
