I have a Murray that was given to me, here is the info from the mower:
On the mower body:-Garden Tractor 18hp/46" Industrial/Commercial Engine
& on the Engine:-14 HP V-Twin OHV Vanguard Model#303777;Type-0032-03 (5349); Code-91020111.
The problem I am having is that when we first started it up, we drove it around the yard and then into the shed with no problems in shifting into all gears. Then, we go to drive it, and it won't go into any gear. It acts like it has no drive at all. Everything seems fine underneath. Can you give me any help at all on this?

The first thing to check is the drive belt from the engine to the trans. It may have broken, jumped of the pulleys or the idler pulley. If that isn't the problem just back back to use for step #2.