Some snakes are picky eaters, and just fast in the winter no matter what. Others are picky about certain types of prey, etc.
Yes, f/t need to be unthawed ten warmed up (warm water or blow dryer are best). This will help with the snake recognizing it as food. I would try this before your snake gets hooked on live. Trust me, if it will take f/t, you want to keep it on f/t.