Can you post a picture of the enclosure including light placement as I'm a little confused as you say you put it over the cooler side. As Grifthegreat stated you need to know exactly what the temperatures are. Have you changed anything recently that could have affected his appetite? Cleaned the enclosure, different substrate, moved the enclosure etc...

With my guy if the enclosure perimeters are good and he's hungry he'll eat. You could try a rat if that's what you were giving him just to see if you can get a feeding response. They're not known for being picky usually.

Good luck.