The community is also a great place to check out. Try this link 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:
If you're encountering issues with launching Aliens vs. Predator, make sure everything installed smoothly.
Exit Steam entirely.
Browse to your Aliens vs. Predator installation folder (Usually C:\Program Files\Steam\steamapps\common\Aliens vs predator\)
Run the following installers:
Reboot your computer and test any issues again. If the issue that you are encountering persists, contact Aliens vs. Predator support.