What are the temps in the hotspot and coldspot? Could be too hot or too cold.
What's the humidity? Although since you mention a screentop, i'm guessing it's very low. If you can't measure it, get a small tupper with a lid, put wet sphagnum moss in it (but not soaking wet), make a hole enough for her/him to get inside/out and put it in her/his tank.
Check it's weight, put it inside the tnak and leave it alone for a couple of days. Try to avoid the temptation of pick it up all the time. Let it calm.
If he eat at least once since you have it, don't panic.