Try live earthworms.
How long has it been warmed up (if you brumated it)?
Also try seperating it from the others for a day and see if it eats better. Some snakes know they are the smallest/weakest, and are afraid to eat if the others are agressive eaters.
If that does not do the trick, consult a vet about parasite treatment. Parasites can make a snake feel icky, and off its feed.
I'm sure others will chime in here with more suggestions!
