Can you ploease help!!

It means the cat has a physical problem and needs to see a Vet. Are there any more kittens? Is the cat in pain, sick?

Dead neonates are difficult to deliver. Before delivery, fully developed kittens are fairly easy to feel, but with one dead kitten, might there be another partially developed one as well? If so, it will cause chronic problems even serious infections if allowed to remain. But first, find out. See the vet for a better evaluation.