Maybe you pruned at a the wrong time or in the wrong way. Its easy to cut off the bits that will flower. Save pruning until early spring and don't cut back more than a few inches beyond last years dead flowers, which should have been left on the bush over winter, until after the last frosts.. If the bush needs reducing in size take a few stems right back each year rather than doing it all in one go.

As already said, if its Hydrangea macrophylla (lacecap or mophead) and you pruned it last year or early this year, that will cause no flowers. They flower on the previous year's wood, so the only pruning that should be done is in spring, after growth begins,when you only remove any dead bits and old flowerheads.

Otherwise, excessive dryness at the root can sometimes cause this problem, or if you've given it too much nitrogen in the form of high nitrogen fertilizer.

Also, hydrangea must have a few hours of sun each day in order to flower. If it's sitting in the shade all day, don't look for flowers.