Thanks for the help, tried all that plus all the usual from Garmin support but it's still not working. I guess it's dead.
It might also help those wanting to help if the OP answered the question in post number 2. Kind of hard to lend help not knowing any symptoms other than it don't work.
When I press the button to pair the sensor the led flashes when the magnet on the crank arm passes but not when the magnet on the wheel passes, and yep I can hear the switch clicking even when it's of the bike as I pass a magnet close to it.