The motor is shot and your opener system (the whole door, tracks, drive, etc.) is likely set up wrong or has worn to the point of complete disfunction.

A garage opener doesn't shear off the drive shaft and sprocket unless the opener isn't centered on the load or the wheels/tracks are binding up. Most garage door openers just stop working like your motor currently is when they wear out.

You should reassess the entire system and just replace the opener.