때문에 implicits negative meaning in some extents. For example, I failed the exam because of you! I failed the exam 너때문에! 때문에 is usually used when sb want to point out the reason why sth happened. And 때문에 is used when usually sth bad happened. If sth good was happened, then you can use 덕분에 For example, Thanx, 니 덕분에 시험 통과했어! (I passed the exam because of your help) But these days kid just use 때문에 for both good meaning and bad meaning. 위해 only means 'for one's sake ' No confuse! :)

Thanx JayJ for the detailed explanation-its the best way for me to learn the language *

"너 때문에" is correct in this sentense, " I didnt come here for you..I came here for myself." If you translate this sentense "There is a present for you.", you can "저기에 너를 위한 선물 있어" As you know, "for" have a lot of meanings. I think that the difference depens on the "for" 's meaning.