Are you pushing the belt with your foot ?
You may have a blown lower board, blown fuse on the lower board
or bad motor brushes. You can test your motor with a 9 volt battery
I have a video on this if you need.
http://www.mindbites.com/lesson/379-how-to-test-a-treadmill-that-wont-start
markepeterson@austin.rr.com
Mark Peterson, March 2008