The idea behind Laplace's Computer is that in principle one can predict the future exactly and accurately. Only a couple of small things are needed. First, the universe must be deterministic. Second, one should know all the forces and laws of nature and be able to model them precisely. Third, one should know all the positions and velocities as well as other properties of each and every item that the universe is composed of. Fourth, one should have a computer with enough computing power to run a model of the universe. Now, given the current state of the universe and the laws of nature, one could compute the future states of the universe.
First I thought I had a big problem with Laplace's Computer. The problem is that when a computation is being executed on a computer, that computation changes the computer's states. And because computer's states are physical things (swarms of electrons), changing computer's states alters the universe. So while computing the future states of the universe, the computer should also take into account how its modeling of the universe will affect the universe. And it should also take into account how "taking into account how its modeling of the universe will affect the universe" affects the universe. And so forth.
So Laplace's Computer cannot work, on the pain of infinite regress, unless--and this is the beautiful part--the computer is not in this universe. Is that a problem to you?