New Hampshire, unlike many other states, does not have a 'lemon law' for used vehicles. That is why there are so many used car dealers on all of the major roads into NH from MA, because MA does have a used car lemon law and the dealers can get away with buying junkers in MA, then selling them in NH.
The only legal protection on the purchase of a used car in NH is that if the used car does not pass an inspection after purchase, then the dealer must accept the car back.
Used cars break down. That's what they do. Unless it was from an intentionally concealed defect which you can prove, or unless you can prove that there is some reason to overcome the "as is" condition on a used car sale, this is difficult. So, without more facts, I don't believe I can offer additional advice.
This answer is provided for informational purposes only. Actual legal advice can only be provided in an office consultation by an attorney licensed in your jurisdiction, with experience in the area of law in which your concern lies.