I was using Sonar Artist when I saw a YouTube video about Melodyne. As near as I can figure, it's available in Sonar Professional and Platinum only. I spent the $150 for the Professional version. I opened a project that had some audio tracks. The Region FX tab doesn't open. How do I go about using Melodyne? What am I missing?

Melodyne is a separate download and install plus registration. You need to follow those steps first and it will then show on your list.

It doesn't show up in the list. I went to my account page and searched there. There's a lot of connected products but none seem to be Melodyne.

It is a separate item not listed under Cakewalk Professional or Platinum. If you recently upgraded, there is a promotion wrapping up. Often when promotions are nearing an end Cakewalk runs out of third party licenses for products like Melodyne and Addictive Drums. This is usually resolved within a few business days. If the product does not appear at the top level of the Command Center or your account after a few days of purchasing, open a case with Cakewalk. If the case is not resolved in a timely manner create a new thread here http://forum.cakewalk.com/Cakewalk-Store-f79.aspx with the case number.