hmmm very strange on this, could be a number of things, as he said ^^^ have a souct, my 1st thought would of been the battery or Alterator but you already said thats fine, it could be that your Starter motor is bugged, try this, open your drivers door, take off the handbreak and pop the car into reverse, then (witht he engine off ofc) rock the car back and forth, if you hear a click, then the car starts fine, you need a new starter motor mate.
Hope this helps
