In order to know how to open it you would need to post the mfg and model number. First troubleshooting things would be, Have you verified there is voltage going to the motor when you depress the open/closed switch? Motor wires should be accesable from the outside stick a pin through them and meter while pressing open/close switch. May be as easy as a blown fuse. Is there any noise coming from the motor? Stripped coupling/broken pin on drive shaft. Got voltage no noise motor is probably kaput.
Brian, Loretta & Daisy (Golden Retriever)
2008 HR Endeavor 40 PDQ , ISL 400
2010 Dodge Ram 1500 Toad