Blades no longer not engage

I have a Craftsman 917.275683 riding mower. I had to put it away till I received a replacement pulley for the blades. Everything is ok, but now the blades don't engage when I pull the PTO switch out. It worked fine when I put it away. Belt tension and routing is good, and the mower runs fine. Me no unnastand what happen! I eagerly await your opinions.