Launching game from my old HDD

[kickingkats]

So I have just bought a new gaming rig and I decided to get a new HDD in the process. I have set the bios to have the new HDD as the main one with its OS and have the old one as just a secondary folder. Now when I go to launch a game that is in the old HDD it says it needs to be installed before it can be played. My question is, if the game is already installed on the old HDD why is it asking me to install it again on the new one (thus defeating the purpose of a secondary HDD)?
Can't the game just launch from the old HDD? the file path is correct and I have access to all my documents and files, it's just when I try to luanch a game (or any application for that matter) it prompts me to install it again.

 

[popatim]

it doesnt mean installed to the harddrive when it says it needs to be installed. It means installed into the operating system.