Did you, perhaps, prune it earlier this year? If you did, you may have pruned this year's flowering shoots. I would let it come through the winter, make sure it gets enough water and give it a feed once you see new growth. Try not to prune it until you see what it does next year?

It may be that they don't get enough sun. I've been trying to get Hydrangeas established in my garden, and although they're growing slowly, they're also slow to produce flowers. I'm sure in my case that they need more light.

Mine flower better in the Sunny part of my garden and are always produing large amounts of flowers, eventhough the tag says shade.

Exactly! Plants can't read, can they!