If your watch is totally empty, it will take a while (15-20 mins) for the watch to show any kind of life.
Use a small 2 Amp, 5 Volt USB wall plug like that for your own phone. If there's no charge, test the USB wall plug with another device at home to make sure that it’s not the issue. Charging from low voltage devices, like computers, will not provide sufficient power.
Charging using high-voltage USB blocks (iPad, laptop charger etc) will cause the watch's battery to drain too quickly.
Check also that the magnetic connectors have full contact. To make sure of this, charge the watch face-down to avoid putting any pressure that may disconnect the magnets.
If that doesn't work, leave it for several hours. If you're still having issues, contact us.
If the watch does start charging, please note you will only be able to interact with the watch once you disconnect the charger.