C.W.
My son started having this problem when he was 3. He would be up until nearly midnight every night and seldom took naps. Then he would wake up at 5:30am. He would be tired during the day, but seemed unable to wind down. It became an issue mainly because after a couple of weeks his moods became difficult to handle. I suspected it was due to the lack of sleep.
For him it was not merely a matter of "laying down the law", since he did not get out of bed, ask for things or play loudly. He would just lie there, tossing and turning for hours.
Finally, his pediatrician recommended a very small dose of Clonidine to help him sleep. Normally I am opposed to medicating children, but I had tried everything else. It took him only about 2 days to adjust to the medication. Since then, he has sleep for 10 hours/night and he is back to his normal, happy self.
Just a suggestion....I hope it works out for you, whatever you choose to do!