"Because" is a conjunction and is followed by a subject + verb.
(He is here BECAUSE Mary told him to come)
"Because of" is a preposition and is followed by a verb+ING or a noun.
(I couldn´t sleep because of the noise)
(He arrived late to work because of watching tv all night long)
(Because of the noise, I couldn´t sleep)
(Because of watching tv all night long, He arrived late to work)