How can I fix my pro-form CR610?

The model number is PCTL55810. About 5 years old. Used only for walking and only about four nights a week for about 45 mins each time. Problem started a while ago. It went for about 20 mins then suddenly stopped. That lasted a few weeks then seemed ok. Now it runs for about two or three mins then stops. No matter how long we wait to start it again same thing happens. Runs for two or three mins then stops. Any ideas or suggestions? Thanks.