John Deere L130 - drive won't engage

So, need a pro's help here. The main drive belt came off the pulley at the rear axle. Dropped the mower, put the belt back on the pulley. Fired the mower up, but now it won't move. There is a little lever behind the rear seat that you can pull backwards to disengage the wheels. Have noticed now that whether his is "in" or "out" the wheels still move freely. Obviously the drive gears aren't engaging now.

Any help narrowing this down?

Thanks.

John Deere L130 - drive won't engage