I own a hard copy of Left 4 Dead but unfortunately it is registered to my old Steam account, which I made several years ago and have since forgotten the password and even the username. Is there a way to enter the CD key and find the account it is attached to?
The only way would be through the email address associated with the account. A reverse-engineering from the CD key to any account name is not possible.
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Yeah it seemed like a long shot. Just thought there might have been some more insight to find – Lord Apricot Mar 8 '13 at 20:58
uncovery's answer is not actually true: there's a legit way to discover, which account your CD-Key belongs to by contacting Steam Support.
You need to mention that you have forgotten your account name and the only proof you have is the CD-Key. Be honest with them and they'll definitely help you.