If you encounter strange behavior while playing a game, one of the first things we recommend is to verify that your game install is not corrupt.
On Steam, you can do this by followign the instructions below:
- Load Steam
- From the Library section, right-click on the game and select "Properties" from the menu.
- Select the "Local Files" tab and click the "Verify integrity of game cache..." button.
- Steam will verify the game's files - this process may take several minutes.
- Once the process is completed, the window will automatically exit, and any files found to be damaged will be re-downloaded by Steam.
More information is available on the Steam support site.