I bought Mafia II on eBay, the Steam version. Not a Steam Key, but the whole game, all files included, but I was told that I need Steam to play it.

I tried adding the game to my Steam library, but it won't play. I also tried executing the game directly but still no success. It just creates a file called "mafia2.exe.4936.STEAMSTART" (the number is always different) in the same folder but doesn't do anything beyond that.

I have a good computer with all the latest stuff installed, and I'm able to run all my other games no problem.

Is there a certain procedure I need to undergo to add a Steam game, or something I could do to get this game to work?

  • 2
    usually you need to find the CD key number or the like and use that to register the game with steam. How are you attempting to add it where you are saying it does not work?
    – James
    Commented Feb 17, 2016 at 19:41
  • 8
    Umm... what exactly did you buy? A disc? If the disc is supposed to be played with steam such disc is useless by now, as the game would be already redeemed in steam. Are you sure you need steam to play with it?
    – Zerjack
    Commented Feb 17, 2016 at 19:46
  • 3
    It sounds like the previous owner already activated the game under their Steam account so you will not be able to add it to yours. A few years back I bought Left 4 Dead on eBay and the seller sent me all of his account info since the game is forever tied to his account. I changed the password to the account so it is effectively mine. This was the only game in his account and no credit card info was stored.
    – MonkeyZeus
    Commented Feb 17, 2016 at 21:48
  • 9
    Would you be able to provide a link to the eBay posting? I think some of the skilled eyeballs on this website will be able to tell you if the seller is a scam-artist or not.
    – MonkeyZeus
    Commented Feb 17, 2016 at 22:00
  • 3
    You got scammed. Mafia II is Steam-only, so you cannot just buy the disc off of eBay or whatever.
    – user79446
    Commented Feb 18, 2016 at 9:57

5 Answers 5


If the game came with a CD key, then instead of using "Add a Non-Steam Game", select the "Activate a Product on Steam" option. Enter the CD key when prompted, and one of a few outcomes will happen:

  1. The game will successfully add, meaning it is a valid CD key that's not been used before
  2. Steam will complain that it's not a valid CD key, which means it's not designed to be used with Steam
  3. Steam will complain that it's a valid key, but has already been used and is no longer redeemable. (Which means you got scammed on eBay)

If it doesn't have a CD key at all, then it's likely not a steam game, although the error message you mentioned would make me think it is a Steam version.

If the game isn't valid on Steam for whatever reason, it seems your only recourse would be to contact the seller for either a valid key, or a refund.

  • 7
    About the "doesn't have Cd key", that is a scam too.
    – ave
    Commented Feb 17, 2016 at 19:54
  • 1
    @ardaozkal There are a few games (excluding Steam of course) that don't use keys, although they are very rare (and maybe I'm thinking of old games), but the concept is still possible however unlikely.
    – Tim S.
    Commented Feb 17, 2016 at 19:58

It sounds like you bought unpacked files for the game, without a key. Unfortunately, this is likely a scam. Additionally, trying to move extracted files and then play the game on a new system frequently results in issues (in my experience, at least). I'm hoping this isn't the case! Try and ask the seller for a CD key or Steam key. If they refuse to provide one, it's likely sham-town


You'll have to buy the game from Steam or a retailer. If you want to play a Steam version of a game, you will have to activate the game on your account. The files themselves won't run the game in many cases due to requiring the Steam client to be running.

Keep in mind that if the person already activated the key and just sent you the files, it won't work, and you will need a new key that hasn't been activated before.


Sorry, but you may be in for a problem. Contact PayPal immediately. I have been victim of this before.

Steam will not allow you to transfer rights for a game, so people buy the game and activate it with their own Steam account and it is permanently theirs whether they keep the disks or not. The activation code will not work for any other account, it gets permanently tied to their own. Calling Steam will not get it fixed. They don't care.

I paid $30 at a store for Half-Life only to find it won't work and that I could have bought it through Steam for only $10.

The only thing that the disk may be useful for is if you have a poor internet speed or cap which makes downloading the game impossible. Yet you would still need to download some substantial decryption keys to make the game playable and you would obviously require the Steam console itself.

Sorry to hear that you got scammed. Best of luck.

  • The point must have been missed by you. The question posed is impossible. You cannot play a secondhand steam game due to companies encryption methods and one time use keys. As others have stated after my post as well,though I believe I addressed the specifics in greater detail as to why and pose potential use for the disk which may or may work presuming they buy the game from steam and download the decryption keys they may not need to download the content on the disks,saving bandwidth... His details clearly show he has steam installed and presumably has the game installed through it...
    – Firobug
    Commented Feb 18, 2016 at 15:52
  • You cannot play a secondhand... - where does the OP mention it was a second hand game? They were simply asking how to add the game to their Steam library. See the accepted answer. Your answer is your personal experience with buying an already redeemed copy, and doesn't answer the question i.e. how can the OP add the game to their game library.
    – user101016
    Commented Feb 18, 2016 at 16:26

As MonkeyZeus pointed out in a comment, once the key is activated on Steam, it's permanently tied to the account. If this is the case, you could technically play the game if the seller gave you the login details to his account. It's unlikely to be the only game on his account, so he probably wouldn't want to do that, plus you'd have to log into a different account for that one game (accounts can't be merged). Additionally, this violates the Steam Subscriber Agreement without explicit permission from Valve (emphasis mine):

You may not sell or charge others for the right to use your Account, or otherwise transfer your Account, nor may you sell, charge others for the right to use, or transfer any Subscriptions other than if and as expressly permitted by this Agreement (including any Subscription Terms or Rules of Use) or as otherwise specifically permitted by Valve.

Also, it's a risky thing to try, since the seller can then claim his account was hacked and get Valve to restore his access, and there's not much you can do about it.

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