'96 Chevy truck power steering problem

My dad's power steering stopped working today. Here's what I checked:

Fluid level -ok
pump turns freely -ok
a fuse (I believe was called power assist or something) -ok

The power steering is not working at all, no noise, but pump turns freely.
Is there someway pump came loose from pulley shaft or something like that, or could there be a collapsed hose stopping fluid flow?

That's the only other things I could think of. Would appreciate any other suggestions.
Thanks