Return the car to the dealer. You are entitled to either a new car to replace the defective one or a refund of the purchase price, including finance charges and taxes. If you choose a refund, the dealer may impose a reasonable charge for your use of the defective vehicle since the date of purchase.
In many states, the consumer may be required to participate in informal dispute resolution procedures (arbitration or mediation) established by the manufacturer. This may be to your advantage. Finally make sure you are dealing with a consumer lawyer who is well versed in lemon law.