There is a couple of things you need to know and do. Know: * You will not necesarilly make it a valid PR7 again. * If you do work hard it may gain pagerank again. Do: * Find out if Google blacklisted the domain. If so, you need to get it fixed with Google. * Once that it done, develop a website and work on it. It may take a long time to get pagerank again, but I doubt you will get a PR7 again.