2 year old ball python won't eat mouse.?

I just got him. The guy who sold him to me said I should feed him today, so i bought frozen mice. took the snake to the store with me, showed the clerk and he told me exactly what size mouse that snake should be eating. I thawed the mouse in warm water for 20 min. made sure it was warm before putting it in tank with snake. the snake responded well. spending at least 3 hours wrapping itself around the mouse. smelling it, licking it. then went in his little house a fell asleep. still wont eat the mouse. the previous owner fed him live mice, so is that a huge issue?