Cheatcodes:

Press " ` " (or tilde) to bring up the console:

TheTrooper ?- God Mode 
SunandSteel -- Refill Ammo. 
DieWithYourBootson -- All Ammo. 
StillLife -- Invisilibility. 
Revelations -- 8 Artillery shoots. 
You should also try to enter this figure of speech: "you've got problems", just like it says here, and change to 3rd person view to see whats happens. Does not work with all versions though.