The CD Key is the 16 digit number found with the box that the CD came in. It is needed to install Wrath.
On the CD Sleeve.
You just need to buy the expansion set and update your account with the CD code and then you are good you dont pay ny additional fees.
The CD key on the case is a code required to register the game to your battle.net account. Once used, it can never be used again. This also means that getting such a code through a website (like answers.com) means nothing and you can't use someone else's code. If you do buy the expansion, keep the CD key, because if your account is ever lost you may need to send a copy of the code to Blizzard to confirm you own the expansion.
If you already have an active Battle.net account with World of Wacraft and The Burning Crusade registered, all you have to do is install Wrath of the Lich King from a CD or Digital Download. You will receive an activation key with your product - when you log in to your Battle.net account, you should see an option to add a game to your account. Use this option to fill in the key and upgrade your existing WoW account to Wrath. If you do not yet have an active account or a WoW account, you will have to buy and install World of Warcraft, make a Battle.net account and also buy and register The Burning Crusade before you can take the steps above.
Warcraft 3 was recently patched to no longer require the CD to start. World of Warcraft as well as The Burning Crusade and Wrath of the Lich King have never required a CD to start. If earlier versions of Warcraft have not been patched to no longer require the CD, you can download a disc imaging program such as Deamon Tools Lite, create a virtual image of your CD, and "mount" the image to run the game, instead of using the CD.
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It is the expansion pack that comes after Wrath of the Lich King. You do not need to purchase the CD/DVD to play as you can download the client which allows you to play as you are downloading (once you download enough of it). Although you do not need a Cataclysm account to play the basic WoW, you do need it to take full advantage of all the Cataclysm features, zones, and races.
UNLESS you are installing Wrath of the Lich king expansion of which there IS only one, there are 6 CDs for WoW, and 4-5 for WoW: Burning Crusade expansion it will need them all, so that might be why, or clear out any unneccesary items on your C: Drive
I suggest you contact the company who made the game to get a new CD key.
its the 20 didgit code at the top of the back of the kanes wraith manuel
i think CD key provide an access to do some thing. it is often used in playing game like wow CD key and ffxi CD key.
The "key" is usually placed on the original CD sleeve or sent separately as in an email or other media. The CD key will not be imbedded anywhere on the CD.