hey yeah i'm having the same sorta problem.... i replaced these little copper clips inside the starter motor (car manual helped out heaps suggest you get one)
then it was fine for about a week now car wont start at all. replaced spark plugs didnt do anything.
booked it into auto electriction tomorrow to get a "booster relay" put in. ($55 bucks)
apperantly its just some litle thing that connects to batter, starter motor, earth and something else. apperntly can fix it. it just boost amount of electricty going to starter motor to help it start.
if thats not it gonna replace spark plug wires (80 bucks)
then if thats not it gonna replace whole starter motor (not sure on cost)
AND IF AFTER ALL THAT DOESNT WORK I INTEND ON CRYING IN MY ROOM LIKE A LITTLE GIRL :'(
hope that gives you a slight idea on what it might be. theres other post's about it on these forums just do a seach for em