father asked what was wrong with me?

father asked what was wrong with me?
为什么不可以说what was the wrong with me,是因为这是固定句式,所以不能加the吗
还有为什么这种情况下what 作宾从的主语,而有的情况却不行,是固定的吗?
究竟什么情况what 可以作主语,什么时候不行啊?