Have you ever opened a block of new clay and you couldn't get it to hold its shape?
Here is what to do when you open a new package of clay; take a small piece, like the size of a marble, and roll it out, twist it and roll it out again. Do this many times. The clay should be conditioned and ready to use.
If it crumbles or won't hold its shape, then add a tiny amount of clay softener. If after you added softener, it becomes soft and pliable, then you have old clay but it is still good.
If after you added the softener, you fold the roll in half and it cracks and won't hold together, then you have damaged clay that is no good. It is possible that your clay was exposed to heat, either in storage or transit. It is impossible to revive damaged clay.