Drum wants to start then trips power

when pushing start button dryer hums and wants to start turning the drum.machine trips out .checked belt and looks ok,maybe alittle loose.idler and spring seem ok but not sure.anybody have any thoughts on this problem.
thanks ron fleming

Sounds like your motor is failing. Get someone to help you, and have them press the start button while you hold in the door switch and turn the drum. If the dryer starts to work it is probably the motor.