I cant register half life platinum pack with steam

Hi, ok here's my problem, I lost the package that my cd came in so in turn I lost my cd-key. when I installed half-life 1 again I used my counter-strike cd-key and it let me continue installing. but when I tried registering my half-life platinom pack with the CS cd-key it works for a second and says:

The CD Key you've entered has already been registered to an existing Steam account, and is therefore invalid. Your subscription to Half-Life Platinum Pack has not been completed.

Now there may be a chance that I installed steam earlier then I can remember on my last computer then when I re-installed it I created a new account.

Probably...I have a platinum pack, and I have the HL key registered to
my account and my friend (un-wittingly) registered my CS key...but both
accounts work fine. He just owes me the cost of CS :smile: