Is the watch fully charged? Does it switch the display on when connected to the wall charger or the USB port of a computer.
If not I would check the connections of the battery inside the watch by screwing out the four little screws, but be aware: the rubber seal is hard to reassable again.
Another failure source could be the micro switch of the on/off button or the mechanical contact of the button and the micro switch.
Btw.: Do you really just bought this model?
