If the brushroll is sticking, it will cause too much friction and put too much strain on the belt. Remove the brushroll and clean all hair, string, and lint from the brushroll bearings. If the vacuum cleaner brush still doesn’t spin after you clean the brushroll, consider replacing the brushroll.
First, test the power switch for continuity to ensure that the brushroll motor is getting power. If the power switch has continuity, ensure that the motor turns freely and is clear of obstructions. If power is getting to the motor, and the motor turns freely, but the motor still won’t run the motor is likely defective.