Mower problem

I bought this mower one year ago from Home Depot. This summer on 6/14/08 I hit one stub from the ground and the mower stopped. I tried to start it again it never started again. I read on internet now the mowers have a soft metal key which in case if you hit something is melting and the mower is not starting without taking out the flywheel and the engine. I gave the mower to repair the key to Manassas and they replaced the soft key, but the mower never started again. I gave it to Home depot in Merrifield and I paid $35 for estimate, they kept it there for one month and then they called me. I came at home depot in Merrifield and they could not find the mower, they said it cannot be repaired. Why was the warranty for engine of 2 years? They gave me back $35. Why the key is made of soft metal? Could not be other way to stop the mower if you hit something, but to have the soft key in the engine? What did Home Depot for their consumers?