I've had issues with poor links with pc's. A few things to try; you may already known them in which case I apologise for mentioning them again:
1)ensure it is fully charged and on the charger.
2)turn off any nearby electrical equipment and move as far from any electrical interference as possible. Anything with an electric motor fridges etc.
3)try using a different pc. My windows10 laptop and android mobile are poor at detecting a fitbit via bluetooth but the ipad works brilliantly
I hope this helps
Hugh
