I was working on one project, and using Melodyne as a Region Effect, I am able to hear sound when clicking on and moving Blobs, but when I went to a different project, I get no sound when clicking on Blobs. If I insert Melodyne in the effects bin, and transfer the audio I am able to hear sound when clicking on Blobs. I've compared both projects, and I'm not seeing any difference between the two projects. Clicking input monitor on and off doesn't do anything.  I don't have any effects on the Melodyne tracks. It's very frustrating. 
 
Thanks,
 
George

There was this one thread that seemed to have a solution, though it seems to be dependant on just toggling some things on and off, here's a link, maybe this will help your situation ?
http://forum.cakewalk.com/Melodyne-Blobno-audio-not-solved-for-me-m3396399.aspx

Hi George. Try toggling the global fx bypass button in the mix module. 

Thank you both! toggling the global fx bypass button worked!

This just started happening and it was driving me crazy having to guess what the problem was, and wasting time listening over and over to make sure the pitch was just right.  Thanks!!!