my new apple watch won't charge

Hi - when charging your watch, check that:

All plastic wrap has been removed from both ends and both sides of the charging cable (check closely on the head of the charger).

• The back of your watch and the head of the charging cable are clean and dry (clean them with a nonabrasive, lint-free cloth).
• The charging head is properly aligned with the back of the watch, with the concave / curved side touching it fully:

  Some watch docks, stands, cases or protectors might hinder this.

• You are using a genuine Apple Magnetic Charging Cable or an Apple certified magnetic charging module.
• If you are charging your watch by plugging into mains power:
  • Check that the USB connector on the Apple Magnetic Charging Cable is pushed fully into the USB Power Adapter.
  • Try using different adapters from the following:
    • The genuine Apple USB Power Adapter that was supplied with the watch, or;
    • A genuine Apple 5W (iPhone) or 12W (iPad) USB Power Adapter, or;
    • An Apple-certified (MFi) third-party 5W USB power adapter.
• If charging via a USB port on a computer, ensure that you use a USB 2.0 or 3.0 port, the computer remains turned on and awake and the cable is plugged directly into the computer (not into, for example, an external keyboard).
• If the battery is very low, you may need to wait for a few minutes before the green lightning bolt appears (confirming that charging has started).

More information:

Check your battery and charge your Apple Watch - Apple Support