I have a used Murray riding mower that does not have a manual. I need to know what adjustment or repair is needed to "engage" the mower blades. Nothing happens when I push the handel forward. I adjusted a screw type device (just above the deck) that increased the torque one time before that solved the problem but that did not help this time.

You may need to replace the belt, it sounds like it has stretched if you have not more adjustment left on the spring tensioner pulley.