The Steam support site is a great place to find comprehensive troubleshooting tips if you're having trouble with a game. Check out the links below to get started:

• Verify Integrity of Game Cache – try this first if parts of the game are missing or the game crashes.
• Windows Vista, 7, and 8 Troubleshooting – learn how to run the game as an administrator, and correct issues due to User Account Control (UAC).
• Antivirus software reports Steam games are malicious – read this is if the game is reported as malicious.
• Programs Which May Interfere with Steam – read this if other programs may be affecting your gameplay.
• Language Settings – learn how to change languages.