What can I do about my snake refusing meals?

I have a young male Argentine boa who is refusing to eat. I have had him for almost a year and have never had problems getting him to eat. I have tried several times over the last month and a half to get him to take frozen/thawed mice, and even offered him a live mouse on one occasion. He "kills" every time, but does nothing but hold it afterward. The vet said he was healthy when I took him for a checkup and he has always been a healthy feeder before this. What should I do?