The return of Sauron

If my memory serves me well, Melkor was able to either evade capture by the other Valar, or manage to worm out of it in the end. He was the most powerful among the Valar in the beginning, who is to say that in his thousands of years confinement he was not able to find a way out of his prison, or if he was imprisoned in a void as for some reason my memory is telling me, who is to say he is not or was not able to utilize the energy of his prison to make himself stronger and break free?