Generally the lack of blooms on a hydrangea indicate improper pruning. When and how to prune a hydrangea depends on the type of plant that you have. There are many types. Look up information on your specific kind of plant.
Some hydrangeas bloom on old wood. These include big leaf and oak leaf. Plants that bloom on old wood usually flower in early summer and form the next year's flowers in late summer and early fall. So prune these in late summer or early fall. Better yet, cut those big, fat gorgeous blooms and put them in a vase!
Hydrangeas that bloom on new growth usually flower bloom in late summer. These include panticle and peegee. Prune these in late winter.
A good pruning can increase the size of the blooms. Some varieties appreciate a hard prune, but it depends on what type of hydrangea that you have in your garden.