Alrighty, not to throw too many people at you but we need you to be as specific as you can be.
Say exactly what buttons you hit, how the screen reacted to it (as Pam did in her post when she described how you can turn both TestingCheats and BuyDebug on), and then what happened after.
Did the game pause? Did the screen darken? Was the space there to type cheats in? Did the game start up again after typing and hitting enter?
The more specific you are, the more we can help you.