Hi,
You actually never needed to buy the game again. Just format your computer (I recommend backing up your profile files, which is in the Forward Development folder in documents).
Step 1: Find the mail from Forward Development with the serial number of your key.
Step 2: After installing CCD again, click on the link that tells you to activate.
Step 3: Put the new product code (should be displayed in the CCD page)
Step 4: Put the [/b] old serial number [/b] where it asks you to.
Step 5: A new key will be generated. You can use it and it will activate your CCD.
PS: If you have an earlier version than 1.3, your key will not work with 1.4.