I have the same problem.
Had a lengthy online chat with Garmin. They were very helpful but the watch could not be fixed. They eventually gave me a code and said I need to use the code to buy another watch from them for 60 pounds (UK) as mine was out of warranty.
They said that perhaps I had disconnected the watch from my pc before completion of course updates (via Garmin Express). They said that even if Garmin Express states that the update was complete I should only disconnect via the hardware removal procedure (i.e. the 'safe to remove' feature) on my pc.