Why is my treadmill shutting off on me?

I have a Sportscraft TX5.0RC. When I get on it....I set the speed but after about 10 seconds it shuts off and under the distance/pulse area it shows a number 3. I never set anything up in distance/pulse nor in time/step area. I only set up speed. Am I missing something here or doing something wrong? I have turned off and unplugged but it is still doing the same thing. Any help would be much appreciated! Thanks!