My versi won't eat...

Hi, I have a versicolor and he hasn't been eating for about 7 weeks now.
I'm doing something wrong but having trouble figuring out what it is!
He's in a 5 gallon tank with a small heating pad under the corner of the
tank, 3" of substrate (it's one of the dehydrated bricks that you soak),
I'm not exactly sure what the humidity level is but I mist the sides of
the tank at least once a day and he has a shallow water dish. When I feed
him crickets he just kills them I think because when I look to see if he's
eaten they are dead but still "intact". If someone could please help me
I'd really appreciate it. Thank you, Toni:)