Drive motor is shorted or de-magnetized causing a high power demand.
Inspect the fan mounted on the lower PCA for dust/debris buildup. Clean if necessary, ensuring the fan spins freely. Some lower PCA's do not have a cooling fan and others may have the fan mounted on the underside of the lower PCA making it not as visible.
The fan was free of dust or debris but does not spin. Make sure that the fan wiring is secure and properly connected to the lower PCA. If no obstruction to the fan and the wiring is good but the fan still doesn't turn, replace the lower PCA.
Check the amp draw using a clamp-on AC volt-amp meter during loaded and no-load conditions; compare the values to a similar treadmill that is known to have a good running belt and deck. Replace the belt and/or deck if necessary. Don't forget, some units have a double-sided deck which means it may be flipped over rather than replaced if it has an unused side.
Test unit with a known good lower PCA. Replace lower PCA if necessary.
Test unit with a known good drive motor. Replace drive motor if necessary.