Popcorn kernels that do not pop do not contain enough water. Water is needed in the starch of the kernel in order to create pressure and eventually pop.
If popcorn is too dry and does not pop, the kernels can be soaked in a little bit of water. The kernels should be covered until they have absorbed all of the water. The kernels should be ready for popping in 48 to 96 hours.
The term for kernels that will not pop is an old maid. Popcorn should not be popped with butter as it will burn and alter the taste of the popcorn.