You should prune hydrangeas after flowering, or in the spring. Have you tested your soil? You may be able to get a soil testing kit to do this (in this country they are about Â£1.50). Hydrangeas tend to do better on neutral to slightly acid soil, also if the soil is moist it's good for them (so a good mulch with rotted manure would probably help if your soil tends to be dry. This would also provide some essential nutrients so if you haven't 'fed' your soil, this could be the answer).
Hydrangeas count as shrubs, so should last for many years. You don't say how long you have had these, but if they are young shrubs they may be just taking their time getting started with the flowers, or maybe they were pruned too hard (when we had our house painted, the climbing hydrangea was cut right down to the ground. It's taken several years to come back in all its glory). Have you had a cold winter? Extreme cold can affect them.
They are superb shrubs (in my opinion) and would be worth keeping if you can get them to perform properly. Hopefully you will!