Is it a heat rock?
It's probably Relocation Stress. Some iguanas need three weeks to a month to acclimate. Make sure he has a hide that he can trust. Make sure he's warm enough at the place he's decided on.
He can go two or more harmless weeks without eating, but he must maintain his hydration. If he won't voluntarily drink water, you may need to syringe it to him. It's actually pretty easy, but give him another week to voluntarily drink.
Check this site, which includes lots of info about eating and hydration issues:
If you can create some kind of moving water, your iguana is more likely to drink. You can use a bowl of some kind with a very small hole in the bottom. Place it on top of the cage, so it drips into his water dish. Two or three drips per minute is good, so you won't have much of an issue with flooding. He will notice the water then.