Entering a code can enable God Mode in Left 4 Dead for Windows PC.
1. From the main menu, select Options.
2. Select Keyboard/Mouse selection.
3. Enable the Allow Developers Console option.
4. When playing the game, press ~ to display the console window.
5. Type Sv_Cheats 1 and press Enter to enable cheat mode.
6. Type god to enable God Mode. You will then be invincible.