Need help with "Portal" game

My Alienware laptop was delivered to my house in November of 2010. It came with Steam and a copy of Portal. Since then, I have re-installed Windows 7 multiple times and I no longer have the game on my hard drive. I still have Steam, but I don't see Portal in my games library as a possible download. I looked it up on the internet but people seem to find fixes or "contact customer support". Do Alienware systems come with a personal product key for Portal? How do I get the game back?

PS: I called Dell who said to call Alienware who said to contact Steam. I have an open support "ticket" reading the following: I bought an Alienware M15x laptop which was delivered to my house around November of 2010. The laptop came pre-installed with Steam and a copy of Portal. I have since re-installed Windows 7 to the computer and would like to know how to recover the Portal game. I did not back it up and it does not appear under my Steam account's "Library."

 

If the game was already activated on Steam under your account, it should show in your games library.
Portal is a Valve game that require Steam. Try to contact Steam Support.

 

If for some reason you cannot get Steam or Dell to give you the key for Portal, it always goes on sale for dirt cheap on the Steam site, during their Halloween, Christmas, Spring, and Summer sales. Typically runs $2-$4 during sales.

 

I'll probably have to end up doing that even though I know that there's a product key out there for me somewhere.