A lawsuit can be closed either by dismissal or because a judgment has been entered. Cases in which a judgment has been entered cannot simply be reopened. The court must set aside the judgment first, and this can be a long, involved legal process. Dismissals are another matter; the case can often be reopened relatively easily, although the exact process varies by state law. A dismissal is made either “with prejudice” or “without prejudice.” This legal language is important, because it indicates whether the closed lawsuit can be reopened at a later point in time.
TL;DR (Too Long; Didn't Read)
You can resume a case that was "dismissed without prejudice" simply by refiling a new case; if the case was dismissed with prejudice, however, you'll need to ask the judge to reconsider the dismissal.
How Was the Case Closed?
Cases dismissed “with prejudice” usually can't be reopened. A judge will only reopen a dismissal with prejudice case under very narrow, specific circumstances. Cases dismissed “without prejudice,” on the other hand, can typically be reopened for any reason. Your first step, then, is to determine how the case you want to reopen was closed. This should be clearly stated in the dismissal order. If you don't have a copy of the order, the court clerk can usually provide the information by phone or in person.
File a New Lawsuit
To restart a "dismissed without prejudice" lawsuit, generally, all you have to do is refile it. The same procedures would apply for refiling as when the case was originally opened. In most states, this involves filing a petition or complaint, then delivering it to the court clerk and and filing it for a fee. It's up to you to make sure a copy of the paperwork is delivered to the other party in the lawsuit. This is called "service" and states have different rules for this, too, depending on the type of case. You might be able to simply mail it, or you might have to have a sheriff's deputy or private process server hand-deliver it.
Be aware, however, that if you filed the original lawsuit near the end of the statute of limitations, your new lawsuit might be outside of the statute. You can make arguments that the statute of limitations was tolled, or put on hold, because of the prior lawsuit, but that can only occur in limited circumstances as set forth in your state's laws and rules.
Ask the Court to Address Prejudice
For dismissed-with-prejudice cases, you'll have to file a motion with the court, asking the judge to reconsider the dismissal. You would typically do this under the same docket or case number as the original case. Cases dismissed with prejudice can only be reopened with a judge’s permission. If you want to file a new suit instead, you can try, but your opponent may attack the new lawsuit on the basis that the prior suit was dismissed with prejudice and the new suit is the same.
If you file a motion for reconsideration, the court will schedule a motion hearing so you and the other party can present arguments for and against setting aside the dismissal. Different states have varying rules regarding motion requests and applicable deadlines for filing them, and there are also different thresholds to meet for a judge to reconsider his own decision. Visit the court clerk and inquire about motion requirements in your area. The opposing parties must be served with copies of the paperwork and the date and time of the hearing after the paperwork is filed and a date is set.
Persuade the Judge in Court
To have a "with prejudice" dismissal reconsidered, you'll have to persuade a judge that her original decision to dismiss the case with prejudice was somehow an error. Most courts have the power to set aside a dismissal with prejudice if a mistake, fraud, or misconduct by the other party occurred during the lawsuit and those bad actions resulted in the dismissal with prejudice. New evidence found that was not previously discovered at the time of the dismissal might also be grounds to reopen a case, but this, too, can vary by state.
Consider Legal Counsel
Setting aside a lawsuit dismissal can be as simple as filing a new petition or complaint, or it can be very complicated and involve intricate legal procedures and arguments. Even a simple "dismissed without prejudice"case can generally only be refiled once. If you want to attempt to file it third time, you would typically have to provide a legally supportable reason to the court rather than simply following standard filing procedures. Consider consulting with an attorney to maximize your chances of success, and to ensure that all the rules and laws in your state are properly followed.