A lack of hydrangea blooms is most often caused by pruning too much or not enough sunlight. Hydrangeas prefer at least four hours of morning sun and little or no pruning. There are many different types of hydrangeas but I assume you are asking about the more common big leaf hydrangea macrophylla. Perhaps you can send an photo and tell me more about the growing conditions of your hydrangea and I can give you some more tips for bountiful blooms.  Keep growing, Marianne Binetti