Hey Keitha.
Three things.
The threads on the drive shaft are stripped. If that’s the case the head will not stay on the shaft, and both parts would need replacement.
The drive shaft itself could be damaged or broken. Replace the drive shaft only, if this is the case.
The clutch may be worn out or damaged, etc. In most cases it’s easier and not terribly expensive simply to replace the clutch, if this is your issue.
Hope this heads you in the right direction. Good Luck!!