what's the matter的意思是：怎么了、发生了什么事、出什么事了、你怎么了。回如果没事的话就说：nothing；如果有事的话就说：nothing, it's just that +你要说的事。

例句：What's the matter with you? you're acting like you struck gold.你怎么啦?你的表现好像发了财。