Lazer Z HP won't move

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.