Hi and welcome to the Forum... we have a resident hydrangea expert luis, who will probably be along in awhile and give a better answer than I can.
But in the meantime, couple things I would wonder about. Have you been pruning them? When (at what point in the season)? Hydrangeas (mostly, depending on variety) set their buds for the following year in late summer. So if you prune after that, you are pruning next year's flowers off. Hydrangeas need little to no pruning. Do you know what variety hydrangea you have?
Have you been fertilizing them? With what? High nitrogen fertilizers can lead to lots of big, very green, leafy growth at the expense of flowering. Are they sitting in the middle of a lawn? Is the lawn fertilized? Since we don't want lawns to bloom, grass fertilizer is high nitrogen, as above.
Where (in Ohio) are you located (Cleveland has quite a different climate from Cincinnati) and what have your winters been like lately? Very harsh winters, especially if your shrubs are in an exposed, unprotected location, can kill the buds, which are just sitting there waiting for the following summer.
But if they are the variety of hydrangea that blooms on "old wood," that is with the flower buds that were set last year, there may be nothing you can do to make it bloom this year. Look at them closely. If they have no buds, they aren't going to flower this year.
hydrangea flower buds in winter: