Hi
Follow the instructions here, including contacting Apple Support (mail-in service may be available, if required), making a Genius Bar reservation or visiting an Apple Authorised Service Provider if necessary:
- Check your battery and charge your Apple Watch - Apple Support
- If your Apple Watch won't charge or it won't turn on - Apple Support
Be sure to use only an Apple or MFi-certified USB power adapter or third-party accessory in conjunction with the Magnetic Charging Cable or Magnetic Charging Dock when charging your Apple Watch.
If you are already doing so, then try using another such cable and/or power adapter, including trying an Apple iPad USB Power Adapter first, if you have access to one, and allowing at least 30 minutes before checking the status of your Apple Watch again.
To check your service and support coverage, enter the serial number here:
- Check Your Service and Support Coverage - Apple Support
- How to find the serial number or IMEI for your Apple Watch - Apple Support
If the issue is not covered under warranty or any other Apple policy, then your Apple Watch may instead be eligible for replacement via chargeable, out-of-warranty service or via AppleCare+, if previously purchased.
Out-of-warranty service prices (and AppleCare+ service fees / excesses) vary by country and by Apple Watch model. Pricing for the US, for example, is detailed here:
Apple Watch Service Pricing - Apple Support
If the steps in the support articles above do not help, then contact Apple Support (mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider for assistance and to establish your available service options, timescales and cost, if any: