In California, a judgment is valid for 10 years, and can be renewed indefinitely. Other States vary from 7 to 25 years. (Federal judgments expire either in 20 years, or at the same time a State judgment would expire – in the State where the Federal judgment was obtained.)
Almost always, if a judgment expires, and was not renewed – it is worthless. (If the judgment debtor successfully files and is granted bankruptcy protection, that kills most judgments.) See our Your Judgment and Bankruptcy article.