Can you turn them by hand, WITH THE UNIT OFF? Has the belt jumped? Are all pulleys free? Is the belt tight? Need a little more info.
From the model number that looks like the model with the deck engagement on the right fender. Possibly a broken engagement cable. they like to break right at the end were the tension springs connects
Had an issue with a customer mowers a few years back, may of been the same model. In his cause his wife was mowing, and heard a pop, and then the deck wouldn't engage. After close examination, found that the frame around the engine mount has stress relieved, and the front of the engine drops about the thickness of a washer. Because of how far the deck drive pulley is located from the engine, it moved the deck drive pulley on the engine back about 3/4 inch. After shimming the front of the engine with a washer, has been working fine since.
Had an issue with a customer mowers a few years back, may of been the same model. In his cause his wife was mowing, and heard a pop, and then the deck wouldn't engage. After close examination, found that the frame around the engine mount has stress relieved, and the front of the engine drops about the thickness of a washer. Because of how far the deck drive pulley is located from the engine, it moved the deck drive pulley on the engine back about 3/4 inch. After shimming the front of the engine with a washer, has been working fine since.
Once the front of his engine dropped it stayed there. Look at the engine, and how it sits on the frame. Does the front of the engine look like its lower than the rear. look at the big pulley on the engine where the deck belt goes. Does it look like it is slightly leaning toward the rear of the mower.