Repairs Scag Freedom Z

I have a Scag Freedom Z. It is a great mower. The other day while my wife was mowing, it just stopped. The engine was running, but it stopped moving. The blade still engages. But when we work the levers to go forward or back it does nothing. I really don't want to haul it in to a shop and I am pretty handy if I knew where to start. Scag's website has very little help on it. Any help or direction here would be appreciated. Thanks!

Sounds like a broke drive belt.