As far as I know, you cant play pre-owned PC games due to the use of CD-keys. Take this from the FAQ on Gamestation's website:
Why can't I buy Pre-owned PC titles?
Many PC titles come with CD keys which register that copy of the game to a specific machine. This effectively prevents us from offering a Pre-owned option on PC games.
If it's old enough (6 years at least), you don't need to enter the CD to any website, all you have to do is enter it during installation. It will not connect to the internet checking if it has been used. Furthermore, what game is it?