Hi
If your Apple Watch will not turn on, try the following steps:
Try starting or, if necessary, force restarting your Apple Watch:
If that does not help, next try charging your watch for around 2 hours, making sure that you follow the charging instructions here:
After that time, if it has not already restarted automatically, remove it from the charger and try restarting it or, if necessary, force restarting it again.
If the issue persists, 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:
More information:
If your Apple Watch won't charge or it won't turn on - Apple Support