mali uromastyx

Question
Hi, my Mali uromastyx hasn't been eating at all for 5 days, I've been giving him the amount of everything he likes that the previous owner told me to give him but he wont eat any of it. He doesn't really come out of his cave unless you pet him but he'll still only back out half way, he also hasn't came out to bask either. Could the size of the tank have an affect on it, because I was only given a small tank and he's an adult

Thanks for helping

Answer
Before I can really effectively answer this, I need DETAILS. :)

How long have you had him?  
What has he been eating? (Describe the complete diet).
What are the exact temperatures in the enclosure (both cool side, and basking spot where the animal would be sitting - a digital thermometer with remote probe is needed for this).
Has he been handled during this time?
How is his weight? (A photo would help).
Exactly how big is his enclosure?  
What is his enclosure furnished with, and what kind of hides does it have?
What area of the house is it in, and has it been moved recently?

There are many possibilities, ranging from stress to illness, so details are important!