Gear Sport: What is the problem if the Gear is not turning on?

If the battery is completely discharged, the Gear cannot be turned on immediately when
the charger is connected.

Allow a depleted battery to charge for a few minutes before turning on the Gear.
Use the charger to charge the battery before using it for the first time.

Use only Samsung-approved chargers, batteries, and cables.

Unapproved chargers or cables can cause the battery to explode or damage the Gear.

And, Before charging the battery, ensure that the charging terminals of the Gear and the wireless charger

dock are free of foreign material, such as sweat, liquid, or dust. Clean the charging terminals with
a soft dry cloth.

If device is not turned on after charging for a enough periods, Visit  Samsung Service Centre with 
the device.