Check for moistures inside the watch, and keep your watch in dry condition. Clean the charging point, and keep the watch charged for at least one hour before you try to press the power button.
Sometimes the watch get over-discharged, and the battery needs to be activated by charging for more than 1 hour. Don't rush and press any button during this period.
If this doesn't help, please submit a ticket or write to us at firstname.lastname@example.org