Alright, for this cheat all you need to do is hold shift+Esc and a box will appear. In this box it will contain:
Give All
Give Some
Infinite Ammo
Complete Level
God Mode
Invisible
Teleport

The box will contain some others but these are the only ones I find that work. Enjoy! I mean it! Enjoy! Or I'll come along with the Mini Gun! Lol