Hi,Welcome to Just Answer, My name isXXXXX will be helping you with your appliance issue today.
this means the centrifugal switch in the motor is shot, unfortunately. Replaced just the centrifugal switch they don't sell it separately you would need to replace the motor to repair this. When you push the start button the motor starts on the motor start windings and then the centrifugal switch takes over and sends power to the run windings in the motor this keeps the motor running, you can order this motor at the following blue link.
http://www.repairclinic.com/PartDetail/Drive-Motor/1256970 I hope this info is useful, I'm also including a link to all the diagrams which will help you when you go to replace it.
diagram link, http://www.searspartsdirect.com/partsdirect/part-model/GE-Parts/Dryer-Parts/Model-DBXR453GA2WW/0432/0151200?pathTaken=&prst=0&shdMod=DBXR453GA2WW
thanks and well wishes, Bryan