Hi Shankar,
Have you tried accessing the Marketplace with different Mendix Studio pro versions, does it work on the other versions or does it never show up?
It might be a network/firewall issue if it never shows up in Studio Pro, if it does show up but not regularly you can consider deleting the marketplace folder in C:\Users\{your-user}\AppData\Local\Mendix (close Mendix Studio first)
With kind regards, Stephan
There is the workaround to go to marketplace.mendix.com, find the module you need, download it. Then in StudioPro, in your app-explorer, right the app-name and select the second option "Import module package".