I changed the spark plug and mower started runs great. I enganged the blades and it was like i hit a rock.I was in my garage and nothing looked too be under it. Stoped the blades right away and know one of the blades is tounching the side of my mower underneith. Iam scared too engage the blades since its touching pretty hard at the end of the blade on the deck. iam so confused?