Assuming that all of your husbandry is correct, (heating, etc) the only real thing that can be done, is to take him to a vet ASAP! It has been several day since you have posted, and I am sorry I couldn't get to you sooner, so I hope that you would have done something already. If all you are doing is correct, and your guy is refusing to eat, the only thing left is serious ailment.
-----
1.0 Bearded Dragons
1.1 Fat tailed geckos

