Today I picked up a used harrow for $25. It looks OK and the thing has been maintained as far as grease in the roller shaft assemblies. I hooked it to my tractor and it will not even start to cut to any depth. I put two concrete blocks on the thing and still not cutting deep, maybe an inch. Now this is on tilled ground. I put my 200 lb son on the blocks and it still wil not cut more then an inchl. Any suggestions?