Actually we don't know, but when there is an object in a sentence with the object markers like 을/를, -내다 is used otherwise -나다.:) 고장나다 > 고장(이) 나다 끝나다 > 끝(이) 나다 고장내다 > 고장(을) 내다 끝내다 > 끝(을) 내다 \^o^/

나다 is used when something happens on its own.. 내다 is used when something was made to happen 일이 끝났다 The job ended. 일을 끝냈다 The job was finished. (someone made it end) 땀이 났다 Someone perspired 땀을 냈다 Someone made perspiration happen. 돈이 났다 Money appeared... someone came upon some money. 돈을 냈다 Someone paid (for something) 열이 났다 Someone had a fever (it happened on its own). 열을 냈다 Something made something hot, gave off heat, got worked up (heated/ angry) As Pascal mentioned, pay attention to the particles 을/ 를.

고장나다 - when it is not working , malfunction 고장내다 - when some one broke something 텔레비전이 고장나다 - TV is not working 누군가 텔레비전을 고장냈어 - someone broke my TV 좋은하루보내세요! :)

나다: active verb 내다: passive verb