You must first work out what's wrong with it.
May be a wiring problem - might be the starter relay - could be the starter motor itself or even the car's battery or battery terminals.
It is often good to develop a trouble statement - what is wrong with what? What is happening that should not be happening - or more usually what is not happening that should be happening.
You might begin by having one person try to start the car and another listen to discover if the starter relay is operating - the starter relay is usually fixed to the starter motor itself and will have a big fat cable running to it.
Good luck...
Peccavi, May 2009
