Find the model number of the treadmill for future reference during repairs. Make sure the device is not plugged in while you attempt any repairs.
Check the troubleshooting guide presented in the owner's manual to determine the issue with the treadmill. Systematically work through each problem to see if the issue can be resolved through simplified troubleshooting techniques.
Read the warranty, if one is in place, to ensure that do-it-yourself repairs will not invalidate the warranty coverage. If there are limits placed on what the treadmill owner can do in terms of repair, contact the manufacturer for further instructions.
If the treadmill will start, walk on it to see if the device turns off and how long it takes to do so. Taking this measure helps to identify if an existing issue is present in the treadmill's speed sensor. If the treadmill turns off before it can even be used, the speed sensor is not getting the signal needed to the computer in order to make the device work. The sensor will need to be replaced.
If the speed sensor needs replacement, the motor cover will have to first be removed. Once the motor cover is off, the speed sensor can be taken out and replaced with a new component. The motor cover should then be resecured.
If the treadmill fails to work after an individual steps onto the device, the dry belt may need to be examined for wear and tear. The treadmill belt may require replacement and it may also require extra lubrication if the lubrication is minimal.
If the treadmill fails to work due to an issue with the belt, pick up an inexpensive lubricant and apply it according to the owner's manual guide.
If the problem remains unresolved, contact a professional repair service or the original manufacturer. It is better to get professional advice than to run the risk of damaging the equipment further or making it so that the equipment is beyond repair.