Yellow

Magnets are like a hole where things with polar attracting forces fall. You then have to pull the magnets out of the hole, requiring the same amount of energy they let off when falling into it.

In your example, imagine a ball trying to roll down a hill, and then something stopping it. It wouldn't just push whatever it's pushing against forever, it would stay in place because it's blocked. You can't pull any energy out of it because it's blocked, there's something in the way. For it to push it would require that thing moving and actually letting some energy to be released from the system.

Basically, thermodynamics is a bitch, and every time you think you've outsmarted it, you're just wrong. If we could gmod our way into infinite energy, we might actually end up with more problems than we solve.

To solve infinite free energy in the real world, look at nuclear, and ignore all the propaganda spread to convince you otherwise.