If you purchased through Steam, it should pass the license through without needing a CD key. If that isn't working, you'll need to work with Steam and Ubisoft customer support to figure out the issue.

dont need a key

Hey NoWind,

Sorry to hear it you cannot access your copy of Prince of Persia The Lost Crown.

In case you haven't resolved it yet, most Ubisoft games purchased on Steam do not require an activation key.
A digital license is pushed to your Ubisoft account when you launch the game in Steam for the first time, and link it to the Ubisoft account.

Once activated this way, the game cannot be activated on another Ubisoft account.

Please download and install the latest version of Ubisoft Connect from its ♥♥♥♥♥♥♥♥ website: Download Ubisoft Connect[www.ubisoft.com]

IMPORTANT! Run Ubisoft Connect and Steam clients as administrator and try again:
Running applications with administrator rights[www.ubisoft.com]

Sometimes you will need to close Ubisoft Connect completely (not just minimise it to the system tray) and then launch the game from Steam, for accounts to link correctly.

Let us know if you have any further questions.