What could the problem be for this? Have a treadmill that's been outside for a while. The cord was chewed up and I have replaced it, but it goes on for a couple seconds then turns off. What could the problem be.

If it was outside, was it under cover? If it was not, then the console circuitry are corroded and not fully up to themselves. If it was under cover, same thing can happen. temperature and humidity, moisture and cold can also impair the performance of the unit. It may be a difficult problem to trace unless you can open the console and see for yourself the state of the printed circuit board/s. If it looks like silvery powder around the IC's (integrated circuits) pins, then tht's some air and moisture damage. If you live by the sea, same thing will happen on appliances left outside. And to find the cable chewed, looks like it's been outside for a long time and may definitely have rust on the circuit board, in other words - moisture damaged. If there is no silver rust (powdered ash-type rust) and the printed circuit board looks clean, then try and locate the treadmill manufacturer or its supplier websites and email them the problem you're having.