If your treadmill is having technical difficulties, you may be able to fix it. Some common problems such as worn belts are easy to change. Others problems require a bit of know-how to fix.
Check the electrical supply. Make sure the treadmill is getting electricity from the outlet. For all the remaining steps, turn off the power supply.
Clean the unit. Dirt can cause friction build up on the belt and cause it operate stiffly. Once the unit is clean, turn the electricity back on and see if this helped. If not, turn the unit back off again.
Examine the speed sensor for dust and dirt buildup as well. Cleaning the electronic sensors should stop jerky treadmill action.
Replace the belt. Follow the manufacturer's directions to remove the hood of the treadmill. Loosen the belt fasteners with a screwdriver. Slip the belt off the machine. Put a new belt on the machine. Be sure the replacement belt is the proper one for your treadmill.
Adjust the belt if you smell something burning. If the smell persists, disconnect the unit and don't use it until you fix the problem. In all likelihood, something is causing the motor to run hot. A misaligned belt is usually the cause.
Change the motor. If all else fails, this may be the only solution to fix your treadmill. Follow the manufacturer's directions carefully.