。
Unable to sleep at night, he looked exhausted and pale.
Literal
Night sleep-[potential-れ]-not-being-[て] he [topic-は] was-exhausted-[and] color-of-face was-bad.
寝れなくて ('being unable to sleep and...') chains into the main predicate via the negative te-form. 顔色が悪い ('have a bad complexion, look pale/sickly') is a fixed expression — 顔色 literally 'face-color' is the word for complexion. Note 寝れる (instead of 寝られる) is the so-called 'ra-nuki' potential form, increasingly accepted but traditionally frowned on.