Susie, have you had the engine computer scanned for trouble codes? That's going to be the first step in diagnosing the problem; anything serious enough that the car stops running will almost certainly generate one or more trouble codes that can point you in the direction of the problem.
Here in the US most auto parts stores will hook up their OBD scanner for free and give you a list of any codes they find. Or if you have a friend or relative with a code reader, you could ask them to scan your car for codes. Worst case a mechanic will do that for you, but of course they'll charge you for it.
Once you have the code or codes, come on back and edit your question to add that information and we'll have a much better chance of being able to help.