I've already used this CD key with another Steam account.

A CD key can only be used with a single Steam account. If you've already registered this CD key with another Steam account, you'll need to use that account to play your game. Note that you can use the same Steam account on several computers (but only one at a time).

• I need help accessing the account that I registered this CD key with.
• I've tried getting help with accessing my old account, but wasn't successful. What are my options?