What's the model number off the back of the base under the handlebars? Seems like it should be a 724 (38050) or an 826 but I'm guessing and you have the machine in front of you.
Could be a lot of things. Could be an open clutch linkage and weak return spring. That would leave the belt somewhat tensioned for some auger rotation without speed or power.
Take off the spark plug cap, open the belt cover and look around. Check the belt and tensioner and move things around in there with the cluch handle up then tapped down.