If you've lost your cd key then you'll have to buy the game again, or work out the solution on your own as Tom's Hardware will not provide you with cd keys. It's against the forum rules. Plus, we have no way of ascertaining whether you lost the key or not.
Sorry, but that's how things roll here.
In any case, your cd key should be on the game manual, cover/ back of the box. You can also try looking into the word and/ or pdf files on the game disc.