Do I need to deactivate the account on my old desktop to see Pro version on new desktop? Currently, even with activation key I am registered with Free version.
Yes, if you have a single seat Pro License, then you need to deactivate it on one computer before you activate it on another.
If it says you are registered with the Free version, then you have used the incorrect activation key. Go to Menu > Help > License and click Deactivate, then Activate and paste in the Pro License activation key. If you have lost the key, you can have it resent to your registered email address from the Lost Activation Key page.