I pod suddenly stopped working, why?

I recently had my i pod playing through a port in my dads car, it has been used for this purpose before, when suddenly in the middle of the first song i played, it started to make a juddering noise, so i unplugged it and discoverd that the screen had frozen, so i reset my ipod, and it did not turn back on, nor has it done so since. Why has this happened and what can I do to fix it, before taking it into a shop.