MY CAR WONT START?

i have a 1.2 16v o2 plate automatice clio.
After the car struggling to start and having dim lights we changed the battery on the car after doing this the car started perfectly twice. the next morning i turned the ignition and the car was wanting to start but there isnt the kick there in order for the car to start up. i have been told that it could be the fuel cut off switch that needs resetting where would i find this