I have troy bilt rider lawn tractor. The engine runs but the deck will not engage. The front and rear gears and neutral works okay. I change the solenoid that had blown. And from that point this trouble started.. what else can I do ?

The deck and the solenoid are unrelated. Check the action of the swing arm on the belt going from the engine to the deck. Also check the belt on the deck. Either a belt is broken or slipped off in most cases.