I'm thinking about perpetual motion..

So I spent the last couple hours thinking about perpetual motion and how, first off you have to start with potential energy and how that can be converted to kinetic energy and came to the conclusion that it seemed about damn near impossible without the use of magnets, but then it wouldn't be perpetual motion, since magnets have to be replaced every thousand years or so, depending on temperature and outside forces. Now I can't stop thinking about it. Self-sustaining machines? It has to be possible. Any thoughts?