I'm not sure why you're having this issue. Mine does that every once in a while, but it usually doesn't stay that way.
Have you tried Lucas Easy Sims 2 Cheats? This program will give you your cheats, even if the cheat window doesn't open.
http://www.aussietopenders-sims2.com/Programs.htmOpen the program, type in your cheats (you'll only have to ever do this once.) Pick a key that you want to associate with it. The program must be open while your game runs (you can minimize it to the task bar)-it's so small though that it won't effect your game play. In game just hit the key combo for the cheat you want.
The cheat window normally pops up, the program enters the cheat and the window disappears. I've found though that even if the cheat window does not pop up the cheat is active until you deactivate it.
It sounds more complicated than it actually is.