Born into a poor family,he was tired.

orn可以是bear的过去分词,也可以作形容词.
表示existing as a result of birth
你的第一个分句本来应该是主系表结构的.
(he was) born into a poor family,（so）he was tired.
由于没有连词and,so连接2个句子,且必须遵循一个句子中不能有两个谓语动词,所以省略第一个分句的主语和系动词.