Lawn Tractor will not go into either forward or reverse

I have a Craftsman Lawn Tractor Model # 917.288515 it is a YT3000. I purchased it in  march of 2012. When I went to use it last the mower would not move forward or backward. This was sudden and worked fine the last time I mowed. I checked the free wheel control and it was engaged. The v drive belt was attached and looked OK but I could not see much of it looking underneath. I have never changed the tires nor towed any carts etc. I cleaned around the transmission and drive belt. Still no luck. The brake and clutch seem to work. The only thing I noticed was when the free wheel lever was engaged the mower would not move backward but would move forward. With the free wheel disengaged it moves in both directions like it should. I purged the system and I got it to run forward  slow but enough that I could cut the grass.  It would go up hills if I zig zagged and sped up when I turned.  Next time I tried to run it would not.  Tried again the next day and it moved forward slow and not backward at all.  I purged it both times.  My guess it is probably the transaxle or the v drive belt.  Any thoughts what I should try first?