One common cause of a jammed garbage disposal is that the blades are not strong enough or there are too many items in the disposal at one time. First, you should run cold water for 15-30 seconds before turning on the disposal, to make sure that water is not trapped inside it. Next, turn the power off and feel if the blades are moving freely by reaching down with your hand. If they are not, remove any items in the disposal by using tongs or pliers. You can also try to take off the rubber donut to see if this fixes the problem.