Tractor Repair: New Holland model 1215 - 692 hours, bush hog, new holland

Question
Tractor unused for 3 years, (was fine when parked). Knowledgeable equip. operator friend has done the following. New battery, flushed and replaced hyd. oil S3., replaced G3 filter, cleaned and lubed all, drained some diesel and replaced. Starts, idles and accelerates fine, all hydraulics fine.  Will not go forward or back when clutch is released.  Bush Hog is attached and performing fine. Any suggestions, please?

Answer
don't know this tractor but if its like the newer model there are a lot of gears to chose from so first make sure they are all engaged
secondly does the tractor attempt to move or is there just nothing at all happening the clutch could be slipping but you would have some movement but it would be weak also the hand brake could be stuck on so check the cable and linkages