My Proform 770(?) stops in the middle of a workout?

After a good 10 - 15 minutes of walking, the treadmill will just stop working when either my wife or I am using it. Now, when I put my dogs on it , the treadmill seems to run fine. I bought this unit used and everything else seems to be fine, and I know it works because I can have my dogs on it for a longer amount of time. Im guessing it has to do with our weight differences, but regardless, I need help in fixing the problem. Also, if you can recommend someone in the South Florida area that offers home repair, that would be great.