Run the Creative Cloud Cleaner Tool and try again.
This issue comes when the Ps app not uninstalled but manually deleted. So when you try to download, it shows you that Ps CC is already installed.
Run the Cleaner tool to remove Ps CC :http://www.adobe.com/support/contact/cscleanertool.html . Restart your system and then try installing Ps again.
Ahh! You are my hero! Thank you SOO much! I was so frustrated.