When did the dark ages start and end?

By the advent of the so-called Renaissance period, in the 14th century. Renaissance was (litterally) the "rebirth" of the philosophy, knowledge and art of the ancient Greeks and Romans.

The term 'dark ages' by the way was coined by the Renaissance people, who looked down on their predecessors who had not recognised the virtues of ancient art, literature and thinking. In reality, it was a period full of developments, it had had the Crusades, and universities and other centers of learning had developed all over Europe.