Make sure you changed it precisely, because even if it's spelt Enablecheats=1, it won't work. It has to be EnableCheats=1, as the line right under the title [Game Options].
Also, make sure it's the button beside one, right above TAB that you're pressing. That's the button that activates the cheats on a standard keyboard.
EDIT: Sorry, Italian. The buttons on your keyboard are msot likely different than mine. It's the tilde sign (~), at any rate.