It appears that the moving parts of the objective(those that go in and out when you zoom) could be damaged.This occures when the camera is dropped-in this case the most you can do is cleaning the moving parts and try gently to shake them or do anything that may unblock it.

Another blame could be the weak batteries or acumulator of your camera.Try get some new batteries or charge the acumulator.

A final thing you could do is reset to default the camera settings.

If any of these won't help, I suggest you should go to a specialised service, cause the problem-more common than you think- could be serious.
Good luck Smitty

TigerFly