It won't play because it is too light.
Each time it plays a game, it loses weight. When it reaches minimum weight it will refuse to play - even if happy hearts are empty.
The only way to make it play is either to try feeding it a meal (not snack or treat) to increase its weight past the min level, then it will play.
Otherwise, you will have to give it a snack to get it to play a game.
Best, etc.
TamaMum