1. sth.+happen+地点/时间,意为某地/某时发生了某事.例如：
An accident happened in that street.
那条街发生了一起事故.
What's happening outside?
外面发生什么事了?
2. sth.+happen to+sb.意为某人出了某事(常指不好的事发生在某人身上).例如：
A car accident happened to him yesterday.
昨天他发生了交通事故.
What happened to you?(=What was wrong / the matter with you?)
你怎么啦?
3. sb.+happen+to do sth.意为某人碰巧做某事.例如：
I happened to meet her in the street.
我碰巧在街上遇见她.
It happened that I was out when he called.
他来访时我碰巧不在.
4. happen为不及物动词,不能用于被动语态.例如,要表示这个故事发生在去年.不能说：The story was happened last year.但可以说：The story happened last year.
5. happen为短暂性动词,不能与表示一段时间的状语连用.例如,要表示这事发生一年了.不能说：This happened for one year.但可以说：This happened one year ago.
6. happen一般用来强调某事发生的偶然性.如要表示事先安排或有准备的事情或活动,则不能用happen,而要用take place.例如：
A sports meeting took place(=was held) in our school last week.上周我校举行了运动会.(不能说：A sports meeting happened in our school last week.)
7.happen to do表示“碰巧、恰好”时的否定形式有两种,即happen not to do与not happen to do
如： I happened not to have any money with me. = I didn't happen to have any money with me.
我碰巧身上没带钱.
楼主的句子应该改成What happend to you? 比较合适
