most have a belt that turns the thrower. Disconnect spark plug and check for foriegn object jamming it. If none, you may just need to tighten the tension adjuster on the belt, as belts tend to stretch with time. If you've had it a while the belt may have broken. Depends on the model how to replace. Suggest you get the manual and look to see if you can do it or you should just have a service person do it. I've fixed 2 (Craftsman and Snapper) in the last week. I'm a doctor, not a repairman so it can be done.
JB, December 2009
