do you have a neighbour that goes out to work or comes back from work at that time.
my son used to wake at 4 every morning and i found it very hard to settle him back down. my health visitor told me, if he has a clean bum and isnt hurt to go in and lie him back down, give him a drink if he has one and leave him to settle himself. if he cries go back in and lie him down and keep doing it, i know its frustrating hearing him cry but at the moment he knows you are going to go in to him so he is waking through habbit.
we brought a disco ball from woolworths for my son and put it on in his room, he was that amazed by the lights that they sent him to sleep.
just remember who's boss without shouting, stay calm