The community is also a great place to check out. Try these places for help from other users:
Please review the Third-Party Game Support topic to determine whether your question should be directed to the game developer or to Steam Support. Sending a support request to the wrong party may result in a delay in processing your request.
Retail CD-Keys for this game cannot be registered through Steam. If you wish to create a shortcut to this game under your Library, instructions can be found here:
An NTFS filesystem is required to run the Witcher 2: Assassins of Kings. If you are running FAT32 you will need to reformat a partition to NTFS for this game to work.
If you're encountering issues when launching or playing The Witcher 2, make sure everything installed correctly.
Exit Steam entirely.
Browse to your The Witcher 2 installation folder (Usually C:\Program Files (x86)\Steam\steamapps\common\the witcher 2\)
Run the following installers:
Reboot your computer and test the issue again. If the issue persists, contact The Witcher 2 support.
The extra content included with the digital premium version of this title is not automatically downloaded with the game.
To access the bonus content, please log into your Steam account and navigate to the Library Tab. In the drop down menu directly under "Library" switch the view of the list to "Tools". Select "The Witcher 2: Bonus Content" and download it by double clicking, or right clicking the listing and selecting "Install Game..."
After the download is complete, you can access the bonus content by either double clicking the entry in the tools list. You can also navigate directly to the installation folder (Default is C:\Program Files (x86)\Steam\steamapps\common\the witcher 2\BonusContent)