how can i fix my cinquecento 900 1994?

fiat cinquecento 900 1994 the problem is starts fine from cold, but after 5 mins of running, when it is switched off it will not re-start, unless left to cool down, and it has been found that the spark has disappeared, it has had new coils and rpm sensor.
can anyone please help as i am scared to drive it now, but i have to go on hols on tues and dont want to be stranded.