I would not try live just yet. If he at least showed interest in a pre-killed, try it AT LEAST once more before you give up, preferably more. Unless you are breeding your own rodents, feeding live is just a pain. If they refuse the meal, you have a rat to take care of for a week, plus you have to go buy one every week. Pre-killed is a good step toward frozen-thawed, which is by far the most convenient. Again, unless you have the convenience of breeding your own rodents, live prey should be a last resort, used only for a snake that absolutely refuses anything else. If you have only had the snake a week, you are not in "last resort" territory quite yet.
Do you happen to know what the snake was eating before you got him? He may have been on f/t and the pre-killed is confusing him.