I just had a new engine put in my Lazer Z HP a couple of days ago.  It was running fine, but all of a sudden today it quit moving.  The engine runs fine and seems to be okay, but nothing happens when I push forward or pull back on the arms.  It happened while mowing.  Just going fine, then all of a sudden it stops moving.  
Is this a hydraulic issue?  What should I look for?
Thanks for all help.