Most of the time, if an item you buy is defective, the defect will show up immediately and you can ask the seller or manufacturer to fix or replace it. If the seller or manufacturer won't fix it, or gives up after one try and the fixed or replaced item is still defective, you'll have to take further steps.
If you haven't fully paid for the item, in some cases you can simply stop paying. However, not all problems or defects are serious enough to allow you to stop making payments. In order to have a good reason to stop payment:
Even if you meet these criteria, withholding payments can be risky. If you are making payments to the manufacturer or seller, they may not agree with your version of events and may sue you for not making payments.
And if you took out a loan to purchase the product, the lender may not care whether it works properly. Even though you may feel that you are in the right, the lender may sue you if you stop making payments. If you aren't sure what to do, consider consulting an attorney.
If the seller refuses to cooperate, see if the seller will agree to mediate the dispute through a community or Better Business Bureau mediation program. If you can't get anywhere informally, you can sue. In many states, you must sue the seller or manufacturer within four years of when you discovered the defect, but in some states it's as little as three years and, in a few, it's 10 or 15 years. How much time you have to sue is also affected by whether you signed a written contract or bought it on a handshake.