I'm sorry that you are having problems with your chipper shredder and I would like to assist you. I think that first thing that should be done is to check for blockages.
Be sure to remove the spark plug prior to any service or repair of this machine!
I have attached images from the manual that show how to replace and adjust the blades, remove the same panels and guards. Do not remove the blades, just see if there is any debris that is stopping the unit from rotating. I think that you will find the cause of the issue here.
If everything is clear, there are a few more things that we can check, but this is the place to start. Be sure to note if any fuel is in the cylinder when you remove the spark plug, a leaky carburetor float seal can also stop the engine from turning too, by filling the cylinder with fuel.
I look forward to assisting you further.