Yep, I had the same problem with my 510. At first it couldn’t sync, then I updated it again and it was totally non-functional. I had to connect it to my laptop and delete all the files off it, then replace them with ones I had saved earlier. It syncs now, although it still has a few problems.

I’m not sure if that’s any use to you though.

Another thing you could try is updating the software via Garmin Web Updater rather than Garmin Express. It seems to work better. Or do a hard reset as per the instruction manual. Good luck :