- daffs are too dry - daffs have had their leaves taken away too soon in previous years - daffs weren't deadheaded the previous year
Any of those ring a bell?
If none of them do, it could be pests! It might be necessary to dig up a bulb or two and have a gander.
I don't know if it's that easy to get them going again once they go like this, unfortunately. You might be best digging them up and starting again in the autumn I'm afraid. But it's obviously worth finding the problem first so that it doesn't happen again.
You take off the old withered flower, including the bulbous bit at the top of the flowering stem. Then you leave the leaves and the rest of the stem to die back naturally. A feed can help bulk them out for the following year.
Check the bulbs are buried deep enough as well - I just read an article that said this can be a factor.
It could be that the bulbs are now too close together just need separating. If a clump of daffodils are allowed to multiply naturally over the years without being divided, the cramped bulbs will produce only foliage and very few flowers (called coming up 'blind').