Fault with 2000 reg ford puma, please help?

basically the last couple of days my car wont start!! i only starts when it wants to. it does not even tick over when turning the key yet all my electrics still work!! i've tried both of my keys and like i say i could work then it doesn't, could it be my immoboliser?? if so has anyone had this problems before and what did you need yo do?